xref: /linux/kernel/workqueue.c (revision 50599e4c68eeea2cb635e763c9c5befa6dc9ab6d)

// SPDX-License-Identifier: GPL-2.0-only
/*
 * kernel/workqueue.c - generic async execution with shared worker pool
 *
 * Copyright (C) 2002		Ingo Molnar
 *
 *   Derived from the taskqueue/keventd code by:
 *     David Woodhouse <dwmw2@infradead.org>
 *     Andrew Morton
 *     Kai Petzke <wpp@marie.physik.tu-berlin.de>
 *     Theodore Ts'o <tytso@mit.edu>
 *
 * Made to use alloc_percpu by Christoph Lameter.
 *
 * Copyright (C) 2010		SUSE Linux Products GmbH
 * Copyright (C) 2010		Tejun Heo <tj@kernel.org>
 *
 * This is the generic async execution mechanism.  Work items as are
 * executed in process context.  The worker pool is shared and
 * automatically managed.  There are two worker pools for each CPU (one for
 * normal work items and the other for high priority ones) and some extra
 * pools for workqueues which are not bound to any specific CPU - the
 * number of these backing pools is dynamic.
 *
 * Please read Documentation/core-api/workqueue.rst for details.
 */

#include <linux/export.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/signal.h>
#include <linux/completion.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/kthread.h>
#include <linux/hardirq.h>
#include <linux/mempolicy.h>
#include <linux/freezer.h>
#include <linux/debug_locks.h>
#include <linux/device/devres.h>
#include <linux/lockdep.h>
#include <linux/idr.h>
#include <linux/jhash.h>
#include <linux/hashtable.h>
#include <linux/rculist.h>
#include <linux/nodemask.h>
#include <linux/moduleparam.h>
#include <linux/uaccess.h>
#include <linux/sched/isolation.h>
#include <linux/sched/debug.h>
#include <linux/nmi.h>
#include <linux/kvm_para.h>
#include <linux/delay.h>
#include <linux/irq_work.h>

#include "workqueue_internal.h"

enum worker_pool_flags {
	/*
	 * worker_pool flags
	 *
	 * A bound pool is either associated or disassociated with its CPU.
	 * While associated (!DISASSOCIATED), all workers are bound to the
	 * CPU and none has %WORKER_UNBOUND set and concurrency management
	 * is in effect.
	 *
	 * While DISASSOCIATED, the cpu may be offline and all workers have
	 * %WORKER_UNBOUND set and concurrency management disabled, and may
	 * be executing on any CPU.  The pool behaves as an unbound one.
	 *
	 * Note that DISASSOCIATED should be flipped only while holding
	 * wq_pool_attach_mutex to avoid changing binding state while
	 * worker_attach_to_pool() is in progress.
	 *
	 * As there can only be one concurrent BH execution context per CPU, a
	 * BH pool is per-CPU and always DISASSOCIATED.
	 */
	POOL_BH			= 1 << 0,	/* is a BH pool */
	POOL_MANAGER_ACTIVE	= 1 << 1,	/* being managed */
	POOL_DISASSOCIATED	= 1 << 2,	/* cpu can't serve workers */
	POOL_BH_DRAINING	= 1 << 3,	/* draining after CPU offline */
};

enum worker_flags {
	/* worker flags */
	WORKER_DIE		= 1 << 1,	/* die die die */
	WORKER_IDLE		= 1 << 2,	/* is idle */
	WORKER_PREP		= 1 << 3,	/* preparing to run works */
	WORKER_CPU_INTENSIVE	= 1 << 6,	/* cpu intensive */
	WORKER_UNBOUND		= 1 << 7,	/* worker is unbound */
	WORKER_REBOUND		= 1 << 8,	/* worker was rebound */

	WORKER_NOT_RUNNING	= WORKER_PREP | WORKER_CPU_INTENSIVE |
				  WORKER_UNBOUND | WORKER_REBOUND,
};

enum work_cancel_flags {
	WORK_CANCEL_DELAYED	= 1 << 0,	/* canceling a delayed_work */
	WORK_CANCEL_DISABLE	= 1 << 1,	/* canceling to disable */
};

enum wq_internal_consts {
	NR_STD_WORKER_POOLS	= 2,		/* # standard pools per cpu */

	UNBOUND_POOL_HASH_ORDER	= 6,		/* hashed by pool->attrs */
	BUSY_WORKER_HASH_ORDER	= 6,		/* 64 pointers */

	MAX_IDLE_WORKERS_RATIO	= 4,		/* 1/4 of busy can be idle */
	IDLE_WORKER_TIMEOUT	= 300 * HZ,	/* keep idle ones for 5 mins */

	MAYDAY_INITIAL_TIMEOUT  = HZ / 100 >= 2 ? HZ / 100 : 2,
						/* call for help after 10ms
						   (min two ticks) */
	MAYDAY_INTERVAL		= HZ / 10,	/* and then every 100ms */
	CREATE_COOLDOWN		= HZ,		/* time to breath after fail */

	RESCUER_BATCH		= 16,		/* process items per turn */

	/*
	 * Rescue workers are used only on emergencies and shared by
	 * all cpus.  Give MIN_NICE.
	 */
	RESCUER_NICE_LEVEL	= MIN_NICE,
	HIGHPRI_NICE_LEVEL	= MIN_NICE,

	WQ_NAME_LEN		= 32,
	WORKER_ID_LEN		= 10 + WQ_NAME_LEN, /* "kworker/R-" + WQ_NAME_LEN */
};

/* Layout of shards within one LLC pod */
struct llc_shard_layout {
	int nr_large_shards;	/* number of large shards (cores_per_shard + 1) */
	int cores_per_shard;	/* base number of cores per default shard */
	int nr_shards;		/* total number of shards */
	/* nr_default shards = (nr_shards - nr_large_shards) */
};

/*
 * We don't want to trap softirq for too long. See MAX_SOFTIRQ_TIME and
 * MAX_SOFTIRQ_RESTART in kernel/softirq.c. These are macros because
 * msecs_to_jiffies() can't be an initializer.
 */
#define BH_WORKER_JIFFIES	msecs_to_jiffies(2)
#define BH_WORKER_RESTARTS	10

/*
 * Structure fields follow one of the following exclusion rules.
 *
 * I: Modifiable by initialization/destruction paths and read-only for
 *    everyone else.
 *
 * P: Preemption protected.  Disabling preemption is enough and should
 *    only be modified and accessed from the local cpu.
 *
 * L: pool->lock protected.  Access with pool->lock held.
 *
 * LN: pool->lock and wq_node_nr_active->lock protected for writes. Either for
 *     reads.
 *
 * K: Only modified by worker while holding pool->lock. Can be safely read by
 *    self, while holding pool->lock or from IRQ context if %current is the
 *    kworker.
 *
 * S: Only modified by worker self.
 *
 * A: wq_pool_attach_mutex protected.
 *
 * PL: wq_pool_mutex protected.
 *
 * PR: wq_pool_mutex protected for writes.  RCU protected for reads.
 *
 * PW: wq_pool_mutex and wq->mutex protected for writes.  Either for reads.
 *
 * PWR: wq_pool_mutex and wq->mutex protected for writes.  Either or
 *      RCU for reads.
 *
 * WQ: wq->mutex protected.
 *
 * WR: wq->mutex protected for writes.  RCU protected for reads.
 *
 * WO: wq->mutex protected for writes. Updated with WRITE_ONCE() and can be read
 *     with READ_ONCE() without locking.
 *
 * MD: wq_mayday_lock protected.
 *
 * WD: Used internally by the watchdog.
 */

/* struct worker is defined in workqueue_internal.h */

struct worker_pool {
	raw_spinlock_t		lock;		/* the pool lock */
	int			cpu;		/* I: the associated cpu */
	int			node;		/* I: the associated node ID */
	int			id;		/* I: pool ID */
	unsigned int		flags;		/* L: flags */

	unsigned long		last_progress_ts;	/* L: last forward progress timestamp */
	bool			cpu_stall;	/* WD: stalled cpu bound pool */

	/*
	 * The counter is incremented in a process context on the associated CPU
	 * w/ preemption disabled, and decremented or reset in the same context
	 * but w/ pool->lock held. The readers grab pool->lock and are
	 * guaranteed to see if the counter reached zero.
	 */
	int			nr_running;

	struct list_head	worklist;	/* L: list of pending works */

	int			nr_workers;	/* L: total number of workers */
	int			nr_idle;	/* L: currently idle workers */

	struct list_head	idle_list;	/* L: list of idle workers */
	struct timer_list	idle_timer;	/* L: worker idle timeout */
	struct work_struct      idle_cull_work; /* L: worker idle cleanup */

	struct timer_list	mayday_timer;	  /* L: SOS timer for workers */

	/* a workers is either on busy_hash or idle_list, or the manager */
	DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);
						/* L: hash of busy workers */

	struct worker		*manager;	/* L: purely informational */
	struct list_head	workers;	/* A: attached workers */

	struct ida		worker_ida;	/* worker IDs for task name */

	struct workqueue_attrs	*attrs;		/* I: worker attributes */
	struct hlist_node	hash_node;	/* PL: unbound_pool_hash node */
	int			refcnt;		/* PL: refcnt for unbound pools */
#ifdef CONFIG_PREEMPT_RT
	spinlock_t		cb_lock;	/* BH worker cancel lock */
#endif
	/*
	 * Destruction of pool is RCU protected to allow dereferences
	 * from get_work_pool().
	 */
	struct rcu_head		rcu;
};

/*
 * Per-pool_workqueue statistics. These can be monitored using
 * tools/workqueue/wq_monitor.py.
 */
enum pool_workqueue_stats {
	PWQ_STAT_STARTED,	/* work items started execution */
	PWQ_STAT_COMPLETED,	/* work items completed execution */
	PWQ_STAT_CPU_TIME,	/* total CPU time consumed */
	PWQ_STAT_CPU_INTENSIVE,	/* wq_cpu_intensive_thresh_us violations */
	PWQ_STAT_CM_WAKEUP,	/* concurrency-management worker wakeups */
	PWQ_STAT_REPATRIATED,	/* unbound workers brought back into scope */
	PWQ_STAT_MAYDAY,	/* maydays to rescuer */
	PWQ_STAT_RESCUED,	/* linked work items executed by rescuer */

	PWQ_NR_STATS,
};

/*
 * The per-pool workqueue.  While queued, bits below WORK_PWQ_SHIFT
 * of work_struct->data are used for flags and the remaining high bits
 * point to the pwq; thus, pwqs need to be aligned at two's power of the
 * number of flag bits.
 */
struct pool_workqueue {
	struct worker_pool	*pool;		/* I: the associated pool */
	struct workqueue_struct *wq;		/* I: the owning workqueue */
	int			work_color;	/* L: current color */
	int			flush_color;	/* L: flushing color */
	int			refcnt;		/* L: reference count */
	int			nr_in_flight[WORK_NR_COLORS];
						/* L: nr of in_flight works */
	bool			plugged;	/* L: execution suspended */

	/*
	 * nr_active management and WORK_STRUCT_INACTIVE:
	 *
	 * When pwq->nr_active >= max_active, new work item is queued to
	 * pwq->inactive_works instead of pool->worklist and marked with
	 * WORK_STRUCT_INACTIVE.
	 *
	 * All work items marked with WORK_STRUCT_INACTIVE do not participate in
	 * nr_active and all work items in pwq->inactive_works are marked with
	 * WORK_STRUCT_INACTIVE. But not all WORK_STRUCT_INACTIVE work items are
	 * in pwq->inactive_works. Some of them are ready to run in
	 * pool->worklist or worker->scheduled. Those work itmes are only struct
	 * wq_barrier which is used for flush_work() and should not participate
	 * in nr_active. For non-barrier work item, it is marked with
	 * WORK_STRUCT_INACTIVE iff it is in pwq->inactive_works.
	 */
	int			nr_active;	/* L: nr of active works */
	struct list_head	inactive_works;	/* L: inactive works */
	struct list_head	pending_node;	/* LN: node on wq_node_nr_active->pending_pwqs */
	struct list_head	pwqs_node;	/* WR: node on wq->pwqs */
	struct list_head	mayday_node;	/* MD: node on wq->maydays */
	struct work_struct	mayday_cursor;	/* L: cursor on pool->worklist */

	u64			stats[PWQ_NR_STATS];

	/*
	 * Release of unbound pwq is punted to a kthread_worker. See put_pwq()
	 * and pwq_release_workfn() for details. pool_workqueue itself is also
	 * RCU protected so that the first pwq can be determined without
	 * grabbing wq->mutex.
	 */
	struct kthread_work	release_work;
	struct rcu_head		rcu;
} __aligned(1 << WORK_STRUCT_PWQ_SHIFT);

/*
 * Structure used to wait for workqueue flush.
 */
struct wq_flusher {
	struct list_head	list;		/* WQ: list of flushers */
	int			flush_color;	/* WQ: flush color waiting for */
	struct completion	done;		/* flush completion */
};

struct wq_device;

/*
 * Unlike in a per-cpu workqueue where max_active limits its concurrency level
 * on each CPU, in an unbound workqueue, max_active applies to the whole system.
 * As sharing a single nr_active across multiple sockets can be very expensive,
 * the counting and enforcement is per NUMA node.
 *
 * The following struct is used to enforce per-node max_active. When a pwq wants
 * to start executing a work item, it should increment ->nr using
 * tryinc_node_nr_active(). If acquisition fails due to ->nr already being over
 * ->max, the pwq is queued on ->pending_pwqs. As in-flight work items finish
 * and decrement ->nr, node_activate_pending_pwq() activates the pending pwqs in
 * round-robin order.
 */
struct wq_node_nr_active {
	int			max;		/* per-node max_active */
	atomic_t		nr;		/* per-node nr_active */
	raw_spinlock_t		lock;		/* nests inside pool locks */
	struct list_head	pending_pwqs;	/* LN: pwqs with inactive works */
};

/*
 * The externally visible workqueue.  It relays the issued work items to
 * the appropriate worker_pool through its pool_workqueues.
 */
struct workqueue_struct {
	struct list_head	pwqs;		/* WR: all pwqs of this wq */
	struct list_head	list;		/* PR: list of all workqueues */

	struct mutex		mutex;		/* protects this wq */
	int			work_color;	/* WQ: current work color */
	int			flush_color;	/* WQ: current flush color */
	atomic_t		nr_pwqs_to_flush; /* flush in progress */
	struct wq_flusher	*first_flusher;	/* WQ: first flusher */
	struct list_head	flusher_queue;	/* WQ: flush waiters */
	struct list_head	flusher_overflow; /* WQ: flush overflow list */

	struct list_head	maydays;	/* MD: pwqs requesting rescue */
	struct worker		*rescuer;	/* MD: rescue worker */

	int			nr_drainers;	/* WQ: drain in progress */

	/* See alloc_workqueue() function comment for info on min/max_active */
	int			max_active;	/* WO: max active works */
	int			min_active;	/* WO: min active works */
	int			saved_max_active; /* WQ: saved max_active */
	int			saved_min_active; /* WQ: saved min_active */

	struct workqueue_attrs	*unbound_attrs;	/* PW: only for unbound wqs */
	struct pool_workqueue __rcu *dfl_pwq;   /* PW: only for unbound wqs */

#ifdef CONFIG_SYSFS
	struct wq_device	*wq_dev;	/* I: for sysfs interface */
#endif
#ifdef CONFIG_LOCKDEP
	char			*lock_name;
	struct lock_class_key	key;
	struct lockdep_map	__lockdep_map;
	struct lockdep_map	*lockdep_map;
#endif
	char			name[WQ_NAME_LEN]; /* I: workqueue name */

	/*
	 * Destruction of workqueue_struct is RCU protected to allow walking
	 * the workqueues list without grabbing wq_pool_mutex.
	 * This is used to dump all workqueues from sysrq.
	 */
	struct rcu_head		rcu;

	/* hot fields used during command issue, aligned to cacheline */
	unsigned int		flags ____cacheline_aligned; /* WQ: WQ_* flags */
	struct pool_workqueue __rcu * __percpu *cpu_pwq; /* I: per-cpu pwqs */
	struct wq_node_nr_active *node_nr_active[]; /* I: per-node nr_active */
};

/*
 * Each pod type describes how CPUs should be grouped for unbound workqueues.
 * See the comment above workqueue_attrs->affn_scope.
 */
struct wq_pod_type {
	int			nr_pods;	/* number of pods */
	cpumask_var_t		*pod_cpus;	/* pod -> cpus */
	int			*pod_node;	/* pod -> node */
	int			*cpu_pod;	/* cpu -> pod */
};

struct work_offq_data {
	u32			pool_id;
	u32			disable;
	u32			flags;
};

static const char * const wq_affn_names[WQ_AFFN_NR_TYPES] = {
	[WQ_AFFN_DFL]		= "default",
	[WQ_AFFN_CPU]		= "cpu",
	[WQ_AFFN_SMT]		= "smt",
	[WQ_AFFN_CACHE]		= "cache",
	[WQ_AFFN_CACHE_SHARD]	= "cache_shard",
	[WQ_AFFN_NUMA]		= "numa",
	[WQ_AFFN_SYSTEM]	= "system",
};

/*
 * Per-cpu work items which run for longer than the following threshold are
 * automatically considered CPU intensive and excluded from concurrency
 * management to prevent them from noticeably delaying other per-cpu work items.
 * ULONG_MAX indicates that the user hasn't overridden it with a boot parameter.
 * The actual value is initialized in wq_cpu_intensive_thresh_init().
 */
static unsigned long wq_cpu_intensive_thresh_us = ULONG_MAX;
module_param_named(cpu_intensive_thresh_us, wq_cpu_intensive_thresh_us, ulong, 0644);
#ifdef CONFIG_WQ_CPU_INTENSIVE_REPORT
static unsigned int wq_cpu_intensive_warning_thresh = 4;
module_param_named(cpu_intensive_warning_thresh, wq_cpu_intensive_warning_thresh, uint, 0644);
#endif

/* see the comment above the definition of WQ_POWER_EFFICIENT */
static bool wq_power_efficient = IS_ENABLED(CONFIG_WQ_POWER_EFFICIENT_DEFAULT);
module_param_named(power_efficient, wq_power_efficient, bool, 0444);

static unsigned int wq_cache_shard_size = 8;
module_param_named(cache_shard_size, wq_cache_shard_size, uint, 0444);

static bool wq_online;			/* can kworkers be created yet? */
static bool wq_topo_initialized __read_mostly = false;

static struct kmem_cache *pwq_cache;

static struct wq_pod_type wq_pod_types[WQ_AFFN_NR_TYPES];
static enum wq_affn_scope wq_affn_dfl = WQ_AFFN_CACHE_SHARD;

/* buf for wq_update_unbound_pod_attrs(), protected by CPU hotplug exclusion */
static struct workqueue_attrs *unbound_wq_update_pwq_attrs_buf;

static DEFINE_MUTEX(wq_pool_mutex);	/* protects pools and workqueues list */
static DEFINE_MUTEX(wq_pool_attach_mutex); /* protects worker attach/detach */
static DEFINE_RAW_SPINLOCK(wq_mayday_lock);	/* protects wq->maydays list */
/* wait for manager to go away */
static struct rcuwait manager_wait = __RCUWAIT_INITIALIZER(manager_wait);

static LIST_HEAD(workqueues);		/* PR: list of all workqueues */
static bool workqueue_freezing;		/* PL: have wqs started freezing? */

/* PL: mirror the cpu_online_mask excluding the CPU in the midst of hotplugging */
static cpumask_var_t wq_online_cpumask;

/* PL&A: allowable cpus for unbound wqs and work items */
static cpumask_var_t wq_unbound_cpumask;

/* PL: user requested unbound cpumask via sysfs */
static cpumask_var_t wq_requested_unbound_cpumask;

/* PL: isolated cpumask to be excluded from unbound cpumask */
static cpumask_var_t wq_isolated_cpumask;

/* for further constrain wq_unbound_cpumask by cmdline parameter*/
static struct cpumask wq_cmdline_cpumask __initdata;

/* CPU where unbound work was last round robin scheduled from this CPU */
static DEFINE_PER_CPU(int, wq_rr_cpu_last);

/*
 * Local execution of unbound work items is no longer guaranteed.  The
 * following always forces round-robin CPU selection on unbound work items
 * to uncover usages which depend on it.
 */
#ifdef CONFIG_DEBUG_WQ_FORCE_RR_CPU
static bool wq_debug_force_rr_cpu = true;
#else
static bool wq_debug_force_rr_cpu = false;
#endif
module_param_named(debug_force_rr_cpu, wq_debug_force_rr_cpu, bool, 0644);

/* to raise softirq for the BH worker pools on other CPUs */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct irq_work [NR_STD_WORKER_POOLS], bh_pool_irq_works);

/* the BH worker pools */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS], bh_worker_pools);

/* the per-cpu worker pools */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS], cpu_worker_pools);

static DEFINE_IDR(worker_pool_idr);	/* PR: idr of all pools */

/* PL: hash of all unbound pools keyed by pool->attrs */
static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);

/* I: attributes used when instantiating standard unbound pools on demand */
static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];

/* I: attributes used when instantiating ordered pools on demand */
static struct workqueue_attrs *ordered_wq_attrs[NR_STD_WORKER_POOLS];

/*
 * I: kthread_worker to release pwq's. pwq release needs to be bounced to a
 * process context while holding a pool lock. Bounce to a dedicated kthread
 * worker to avoid A-A deadlocks.
 */
static struct kthread_worker *pwq_release_worker __ro_after_init;

struct workqueue_struct *system_wq __ro_after_init;
EXPORT_SYMBOL(system_wq);
struct workqueue_struct *system_percpu_wq __ro_after_init;
EXPORT_SYMBOL(system_percpu_wq);
struct workqueue_struct *system_highpri_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_highpri_wq);
struct workqueue_struct *system_long_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_long_wq);
struct workqueue_struct *system_unbound_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_unbound_wq);
struct workqueue_struct *system_dfl_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_dfl_wq);
struct workqueue_struct *system_freezable_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_freezable_wq);
struct workqueue_struct *system_power_efficient_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_power_efficient_wq);
struct workqueue_struct *system_freezable_power_efficient_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_freezable_power_efficient_wq);
struct workqueue_struct *system_bh_wq;
EXPORT_SYMBOL_GPL(system_bh_wq);
struct workqueue_struct *system_bh_highpri_wq;
EXPORT_SYMBOL_GPL(system_bh_highpri_wq);
struct workqueue_struct *system_dfl_long_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_dfl_long_wq);

static int worker_thread(void *__worker);
static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
static void show_pwq(struct pool_workqueue *pwq);
static void show_one_worker_pool(struct worker_pool *pool);

#define CREATE_TRACE_POINTS
#include <trace/events/workqueue.h>

#define assert_rcu_or_pool_mutex()					\
	RCU_LOCKDEP_WARN(!rcu_read_lock_any_held() &&			\
			 !lockdep_is_held(&wq_pool_mutex),		\
			 "RCU or wq_pool_mutex should be held")

#define for_each_bh_worker_pool(pool, cpu)				\
	for ((pool) = &per_cpu(bh_worker_pools, cpu)[0];		\
	     (pool) < &per_cpu(bh_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
	     (pool)++)

#define for_each_cpu_worker_pool(pool, cpu)				\
	for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0];		\
	     (pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
	     (pool)++)

/**
 * for_each_pool - iterate through all worker_pools in the system
 * @pool: iteration cursor
 * @pi: integer used for iteration
 *
 * This must be called either with wq_pool_mutex held or RCU read
 * locked.  If the pool needs to be used beyond the locking in effect, the
 * caller is responsible for guaranteeing that the pool stays online.
 *
 * The if/else clause exists only for the lockdep assertion and can be
 * ignored.
 */
#define for_each_pool(pool, pi)						\
	idr_for_each_entry(&worker_pool_idr, pool, pi)			\
		if (({ assert_rcu_or_pool_mutex(); false; })) { }	\
		else

/**
 * for_each_pool_worker - iterate through all workers of a worker_pool
 * @worker: iteration cursor
 * @pool: worker_pool to iterate workers of
 *
 * This must be called with wq_pool_attach_mutex.
 *
 * The if/else clause exists only for the lockdep assertion and can be
 * ignored.
 */
#define for_each_pool_worker(worker, pool)				\
	list_for_each_entry((worker), &(pool)->workers, node)		\
		if (({ lockdep_assert_held(&wq_pool_attach_mutex); false; })) { } \
		else

/**
 * for_each_pwq - iterate through all pool_workqueues of the specified workqueue
 * @pwq: iteration cursor
 * @wq: the target workqueue
 *
 * This must be called either with wq->mutex held or RCU read locked.
 * If the pwq needs to be used beyond the locking in effect, the caller is
 * responsible for guaranteeing that the pwq stays online.
 *
 * The if/else clause exists only for the lockdep assertion and can be
 * ignored.
 */
#define for_each_pwq(pwq, wq)						\
	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,		\
				 lockdep_is_held(&(wq->mutex)))

#ifdef CONFIG_DEBUG_OBJECTS_WORK

static const struct debug_obj_descr work_debug_descr;

static void *work_debug_hint(void *addr)
{
	return ((struct work_struct *) addr)->func;
}

static bool work_is_static_object(void *addr)
{
	struct work_struct *work = addr;

	return test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work));
}

/*
 * fixup_init is called when:
 * - an active object is initialized
 */
static bool work_fixup_init(void *addr, enum debug_obj_state state)
{
	struct work_struct *work = addr;

	switch (state) {
	case ODEBUG_STATE_ACTIVE:
		cancel_work_sync(work);
		debug_object_init(work, &work_debug_descr);
		return true;
	default:
		return false;
	}
}

/*
 * fixup_free is called when:
 * - an active object is freed
 */
static bool work_fixup_free(void *addr, enum debug_obj_state state)
{
	struct work_struct *work = addr;

	switch (state) {
	case ODEBUG_STATE_ACTIVE:
		cancel_work_sync(work);
		debug_object_free(work, &work_debug_descr);
		return true;
	default:
		return false;
	}
}

static const struct debug_obj_descr work_debug_descr = {
	.name		= "work_struct",
	.debug_hint	= work_debug_hint,
	.is_static_object = work_is_static_object,
	.fixup_init	= work_fixup_init,
	.fixup_free	= work_fixup_free,
};

static inline void debug_work_activate(struct work_struct *work)
{
	debug_object_activate(work, &work_debug_descr);
}

static inline void debug_work_deactivate(struct work_struct *work)
{
	debug_object_deactivate(work, &work_debug_descr);
}

void __init_work(struct work_struct *work, int onstack)
{
	if (onstack)
		debug_object_init_on_stack(work, &work_debug_descr);
	else
		debug_object_init(work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(__init_work);

void destroy_work_on_stack(struct work_struct *work)
{
	debug_object_free(work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_work_on_stack);

void destroy_delayed_work_on_stack(struct delayed_work *work)
{
	timer_destroy_on_stack(&work->timer);
	debug_object_free(&work->work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_delayed_work_on_stack);

#else
static inline void debug_work_activate(struct work_struct *work) { }
static inline void debug_work_deactivate(struct work_struct *work) { }
#endif

/**
 * worker_pool_assign_id - allocate ID and assign it to @pool
 * @pool: the pool pointer of interest
 *
 * Returns 0 if ID in [0, WORK_OFFQ_POOL_NONE) is allocated and assigned
 * successfully, -errno on failure.
 */
static int worker_pool_assign_id(struct worker_pool *pool)
{
	int ret;

	lockdep_assert_held(&wq_pool_mutex);

	ret = idr_alloc(&worker_pool_idr, pool, 0, WORK_OFFQ_POOL_NONE,
			GFP_KERNEL);
	if (ret >= 0) {
		pool->id = ret;
		return 0;
	}
	return ret;
}

static struct pool_workqueue __rcu **
unbound_pwq_slot(struct workqueue_struct *wq, int cpu)
{
       if (cpu >= 0)
               return per_cpu_ptr(wq->cpu_pwq, cpu);
       else
               return &wq->dfl_pwq;
}

/* @cpu < 0 for dfl_pwq */
static struct pool_workqueue *unbound_pwq(struct workqueue_struct *wq, int cpu)
{
	return rcu_dereference_check(*unbound_pwq_slot(wq, cpu),
				     lockdep_is_held(&wq_pool_mutex) ||
				     lockdep_is_held(&wq->mutex));
}

/**
 * unbound_effective_cpumask - effective cpumask of an unbound workqueue
 * @wq: workqueue of interest
 *
 * @wq->unbound_attrs->cpumask contains the cpumask requested by the user which
 * is masked with wq_unbound_cpumask to determine the effective cpumask. The
 * default pwq is always mapped to the pool with the current effective cpumask.
 */
static struct cpumask *unbound_effective_cpumask(struct workqueue_struct *wq)
{
	return unbound_pwq(wq, -1)->pool->attrs->__pod_cpumask;
}

static unsigned int work_color_to_flags(int color)
{
	return color << WORK_STRUCT_COLOR_SHIFT;
}

static int get_work_color(unsigned long work_data)
{
	return (work_data >> WORK_STRUCT_COLOR_SHIFT) &
		((1 << WORK_STRUCT_COLOR_BITS) - 1);
}

static int work_next_color(int color)
{
	return (color + 1) % WORK_NR_COLORS;
}

static unsigned long pool_offq_flags(struct worker_pool *pool)
{
	return (pool->flags & POOL_BH) ? WORK_OFFQ_BH : 0;
}

/*
 * While queued, %WORK_STRUCT_PWQ is set and non flag bits of a work's data
 * contain the pointer to the queued pwq.  Once execution starts, the flag
 * is cleared and the high bits contain OFFQ flags and pool ID.
 *
 * set_work_pwq(), set_work_pool_and_clear_pending() and mark_work_canceling()
 * can be used to set the pwq, pool or clear work->data. These functions should
 * only be called while the work is owned - ie. while the PENDING bit is set.
 *
 * get_work_pool() and get_work_pwq() can be used to obtain the pool or pwq
 * corresponding to a work.  Pool is available once the work has been
 * queued anywhere after initialization until it is sync canceled.  pwq is
 * available only while the work item is queued.
 */
static inline void set_work_data(struct work_struct *work, unsigned long data)
{
	WARN_ON_ONCE(!work_pending(work));
	atomic_long_set(&work->data, data | work_static(work));
}

static void set_work_pwq(struct work_struct *work, struct pool_workqueue *pwq,
			 unsigned long flags)
{
	set_work_data(work, (unsigned long)pwq | WORK_STRUCT_PENDING |
		      WORK_STRUCT_PWQ | flags);
}

static void set_work_pool_and_keep_pending(struct work_struct *work,
					   int pool_id, unsigned long flags)
{
	set_work_data(work, ((unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT) |
		      WORK_STRUCT_PENDING | flags);
}

static void set_work_pool_and_clear_pending(struct work_struct *work,
					    int pool_id, unsigned long flags)
{
	/*
	 * The following wmb is paired with the implied mb in
	 * test_and_set_bit(PENDING) and ensures all updates to @work made
	 * here are visible to and precede any updates by the next PENDING
	 * owner.
	 */
	smp_wmb();
	set_work_data(work, ((unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT) |
		      flags);
	/*
	 * The following mb guarantees that previous clear of a PENDING bit
	 * will not be reordered with any speculative LOADS or STORES from
	 * work->current_func, which is executed afterwards.  This possible
	 * reordering can lead to a missed execution on attempt to queue
	 * the same @work.  E.g. consider this case:
	 *
	 *   CPU#0                         CPU#1
	 *   ----------------------------  --------------------------------
	 *
	 * 1  STORE event_indicated
	 * 2  queue_work_on() {
	 * 3    test_and_set_bit(PENDING)
	 * 4 }                             set_..._and_clear_pending() {
	 * 5                                 set_work_data() # clear bit
	 * 6                                 smp_mb()
	 * 7                               work->current_func() {
	 * 8				      LOAD event_indicated
	 *				   }
	 *
	 * Without an explicit full barrier speculative LOAD on line 8 can
	 * be executed before CPU#0 does STORE on line 1.  If that happens,
	 * CPU#0 observes the PENDING bit is still set and new execution of
	 * a @work is not queued in a hope, that CPU#1 will eventually
	 * finish the queued @work.  Meanwhile CPU#1 does not see
	 * event_indicated is set, because speculative LOAD was executed
	 * before actual STORE.
	 */
	smp_mb();
}

static inline struct pool_workqueue *work_struct_pwq(unsigned long data)
{
	return (struct pool_workqueue *)(data & WORK_STRUCT_PWQ_MASK);
}

static struct pool_workqueue *get_work_pwq(struct work_struct *work)
{
	unsigned long data = atomic_long_read(&work->data);

	if (data & WORK_STRUCT_PWQ)
		return work_struct_pwq(data);
	else
		return NULL;
}

/**
 * get_work_pool - return the worker_pool a given work was associated with
 * @work: the work item of interest
 *
 * Pools are created and destroyed under wq_pool_mutex, and allows read
 * access under RCU read lock.  As such, this function should be
 * called under wq_pool_mutex or inside of a rcu_read_lock() region.
 *
 * All fields of the returned pool are accessible as long as the above
 * mentioned locking is in effect.  If the returned pool needs to be used
 * beyond the critical section, the caller is responsible for ensuring the
 * returned pool is and stays online.
 *
 * Return: The worker_pool @work was last associated with.  %NULL if none.
 */
static struct worker_pool *get_work_pool(struct work_struct *work)
{
	unsigned long data = atomic_long_read(&work->data);
	int pool_id;

	assert_rcu_or_pool_mutex();

	if (data & WORK_STRUCT_PWQ)
		return work_struct_pwq(data)->pool;

	pool_id = data >> WORK_OFFQ_POOL_SHIFT;
	if (pool_id == WORK_OFFQ_POOL_NONE)
		return NULL;

	return idr_find(&worker_pool_idr, pool_id);
}

static unsigned long shift_and_mask(unsigned long v, u32 shift, u32 bits)
{
	return (v >> shift) & ((1U << bits) - 1);
}

static void work_offqd_unpack(struct work_offq_data *offqd, unsigned long data)
{
	WARN_ON_ONCE(data & WORK_STRUCT_PWQ);

	offqd->pool_id = shift_and_mask(data, WORK_OFFQ_POOL_SHIFT,
					WORK_OFFQ_POOL_BITS);
	offqd->disable = shift_and_mask(data, WORK_OFFQ_DISABLE_SHIFT,
					WORK_OFFQ_DISABLE_BITS);
	offqd->flags = data & WORK_OFFQ_FLAG_MASK;
}

static unsigned long work_offqd_pack_flags(struct work_offq_data *offqd)
{
	return ((unsigned long)offqd->disable << WORK_OFFQ_DISABLE_SHIFT) |
		((unsigned long)offqd->flags);
}

/*
 * Policy functions.  These define the policies on how the global worker
 * pools are managed.  Unless noted otherwise, these functions assume that
 * they're being called with pool->lock held.
 */

/*
 * Need to wake up a worker?  Called from anything but currently
 * running workers.
 *
 * Note that, because unbound workers never contribute to nr_running, this
 * function will always return %true for unbound pools as long as the
 * worklist isn't empty.
 */
static bool need_more_worker(struct worker_pool *pool)
{
	return !list_empty(&pool->worklist) && !pool->nr_running;
}

/* Can I start working?  Called from busy but !running workers. */
static bool may_start_working(struct worker_pool *pool)
{
	return pool->nr_idle;
}

/* Do I need to keep working?  Called from currently running workers. */
static bool keep_working(struct worker_pool *pool)
{
	return !list_empty(&pool->worklist) && (pool->nr_running <= 1);
}

/* Do we need a new worker?  Called from manager. */
static bool need_to_create_worker(struct worker_pool *pool)
{
	return need_more_worker(pool) && !may_start_working(pool);
}

/* Do we have too many workers and should some go away? */
static bool too_many_workers(struct worker_pool *pool)
{
	bool managing = pool->flags & POOL_MANAGER_ACTIVE;
	int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
	int nr_busy = pool->nr_workers - nr_idle;

	return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;
}

/**
 * worker_set_flags - set worker flags and adjust nr_running accordingly
 * @worker: self
 * @flags: flags to set
 *
 * Set @flags in @worker->flags and adjust nr_running accordingly.
 */
static inline void worker_set_flags(struct worker *worker, unsigned int flags)
{
	struct worker_pool *pool = worker->pool;

	lockdep_assert_held(&pool->lock);

	/* If transitioning into NOT_RUNNING, adjust nr_running. */
	if ((flags & WORKER_NOT_RUNNING) &&
	    !(worker->flags & WORKER_NOT_RUNNING)) {
		pool->nr_running--;
	}

	worker->flags |= flags;
}

/**
 * worker_clr_flags - clear worker flags and adjust nr_running accordingly
 * @worker: self
 * @flags: flags to clear
 *
 * Clear @flags in @worker->flags and adjust nr_running accordingly.
 */
static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
{
	struct worker_pool *pool = worker->pool;
	unsigned int oflags = worker->flags;

	lockdep_assert_held(&pool->lock);

	worker->flags &= ~flags;

	/*
	 * If transitioning out of NOT_RUNNING, increment nr_running.  Note
	 * that the nested NOT_RUNNING is not a noop.  NOT_RUNNING is mask
	 * of multiple flags, not a single flag.
	 */
	if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
		if (!(worker->flags & WORKER_NOT_RUNNING))
			pool->nr_running++;
}

/* Return the first idle worker.  Called with pool->lock held. */
static struct worker *first_idle_worker(struct worker_pool *pool)
{
	if (unlikely(list_empty(&pool->idle_list)))
		return NULL;

	return list_first_entry(&pool->idle_list, struct worker, entry);
}

/**
 * worker_enter_idle - enter idle state
 * @worker: worker which is entering idle state
 *
 * @worker is entering idle state.  Update stats and idle timer if
 * necessary.
 *
 * LOCKING:
 * raw_spin_lock_irq(pool->lock).
 */
static void worker_enter_idle(struct worker *worker)
{
	struct worker_pool *pool = worker->pool;

	if (WARN_ON_ONCE(worker->flags & WORKER_IDLE) ||
	    WARN_ON_ONCE(!list_empty(&worker->entry) &&
			 (worker->hentry.next || worker->hentry.pprev)))
		return;

	/* can't use worker_set_flags(), also called from create_worker() */
	worker->flags |= WORKER_IDLE;
	pool->nr_idle++;
	worker->last_active = jiffies;

	/* idle_list is LIFO */
	list_add(&worker->entry, &pool->idle_list);

	if (too_many_workers(pool) && !timer_pending(&pool->idle_timer))
		mod_timer(&pool->idle_timer, jiffies + IDLE_WORKER_TIMEOUT);

	/* Sanity check nr_running. */
	WARN_ON_ONCE(pool->nr_workers == pool->nr_idle && pool->nr_running);
}

/**
 * worker_leave_idle - leave idle state
 * @worker: worker which is leaving idle state
 *
 * @worker is leaving idle state.  Update stats.
 *
 * LOCKING:
 * raw_spin_lock_irq(pool->lock).
 */
static void worker_leave_idle(struct worker *worker)
{
	struct worker_pool *pool = worker->pool;

	if (WARN_ON_ONCE(!(worker->flags & WORKER_IDLE)))
		return;
	worker_clr_flags(worker, WORKER_IDLE);
	pool->nr_idle--;
	list_del_init(&worker->entry);
}

/**
 * find_worker_executing_work - find worker which is executing a work
 * @pool: pool of interest
 * @work: work to find worker for
 *
 * Find a worker which is executing @work on @pool by searching
 * @pool->busy_hash which is keyed by the address of @work.  For a worker
 * to match, its current execution should match the address of @work and
 * its work function.  This is to avoid unwanted dependency between
 * unrelated work executions through a work item being recycled while still
 * being executed.
 *
 * This is a bit tricky.  A work item may be freed once its execution
 * starts and nothing prevents the freed area from being recycled for
 * another work item.  If the same work item address ends up being reused
 * before the original execution finishes, workqueue will identify the
 * recycled work item as currently executing and make it wait until the
 * current execution finishes, introducing an unwanted dependency.
 *
 * This function checks the work item address and work function to avoid
 * false positives.  Note that this isn't complete as one may construct a
 * work function which can introduce dependency onto itself through a
 * recycled work item.  Well, if somebody wants to shoot oneself in the
 * foot that badly, there's only so much we can do, and if such deadlock
 * actually occurs, it should be easy to locate the culprit work function.
 *
 * CONTEXT:
 * raw_spin_lock_irq(pool->lock).
 *
 * Return:
 * Pointer to worker which is executing @work if found, %NULL
 * otherwise.
 */
static struct worker *find_worker_executing_work(struct worker_pool *pool,
						 struct work_struct *work)
{
	struct worker *worker;

	hash_for_each_possible(pool->busy_hash, worker, hentry,
			       (unsigned long)work)
		if (worker->current_work == work &&
		    worker->current_func == work->func)
			return worker;

	return NULL;
}

static void mayday_cursor_func(struct work_struct *work)
{
	/* should not be processed, only for marking position */
	BUG();
}

/**
 * move_linked_works - move linked works to a list
 * @work: start of series of works to be scheduled
 * @head: target list to append @work to
 * @nextp: out parameter for nested worklist walking
 *
 * Schedule linked works starting from @work to @head. Work series to be
 * scheduled starts at @work and includes any consecutive work with
 * WORK_STRUCT_LINKED set in its predecessor. See assign_work() for details on
 * @nextp.
 *
 * CONTEXT:
 * raw_spin_lock_irq(pool->lock).
 */
static void move_linked_works(struct work_struct *work, struct list_head *head,
			      struct work_struct **nextp)
{
	struct work_struct *n;

	/*
	 * Linked worklist will always end before the end of the list,
	 * use NULL for list head.
	 */
	list_for_each_entry_safe_from(work, n, NULL, entry) {
		list_move_tail(&work->entry, head);
		if (!(*work_data_bits(work) & WORK_STRUCT_LINKED))
			break;
	}

	/*
	 * If we're already inside safe list traversal and have moved
	 * multiple works to the scheduled queue, the next position
	 * needs to be updated.
	 */
	if (nextp)
		*nextp = n;
}

/**
 * assign_work - assign a work item and its linked work items to a worker
 * @work: work to assign
 * @worker: worker to assign to
 * @nextp: out parameter for nested worklist walking
 *
 * Assign @work and its linked work items to @worker. If @work is already being
 * executed by another worker in the same pool, it'll be punted there.
 *
 * If @nextp is not NULL, it's updated to point to the next work of the last
 * scheduled work. This allows assign_work() to be nested inside
 * list_for_each_entry_safe().
 *
 * Returns %true if @work was successfully assigned to @worker. %false if @work
 * was punted to another worker already executing it.
 */
static bool assign_work(struct work_struct *work, struct worker *worker,
			struct work_struct **nextp)
{
	struct worker_pool *pool = worker->pool;
	struct worker *collision;

	lockdep_assert_held(&pool->lock);

	/* The cursor work should not be processed */
	if (unlikely(work->func == mayday_cursor_func)) {
		/* only worker_thread() can possibly take this branch */
		WARN_ON_ONCE(worker->rescue_wq);
		if (nextp)
			*nextp = list_next_entry(work, entry);
		list_del_init(&work->entry);
		return false;
	}

	/*
	 * A single work shouldn't be executed concurrently by multiple workers.
	 * __queue_work() ensures that @work doesn't jump to a different pool
	 * while still running in the previous pool. Here, we should ensure that
	 * @work is not executed concurrently by multiple workers from the same
	 * pool. Check whether anyone is already processing the work. If so,
	 * defer the work to the currently executing one.
	 */
	collision = find_worker_executing_work(pool, work);
	if (unlikely(collision)) {
		move_linked_works(work, &collision->scheduled, nextp);
		return false;
	}

	move_linked_works(work, &worker->scheduled, nextp);
	return true;
}

static struct irq_work *bh_pool_irq_work(struct worker_pool *pool)
{
	int high = pool->attrs->nice == HIGHPRI_NICE_LEVEL ? 1 : 0;

	return &per_cpu(bh_pool_irq_works, pool->cpu)[high];
}

static void kick_bh_pool(struct worker_pool *pool)
{
#ifdef CONFIG_SMP
	/* see drain_dead_softirq_workfn() for BH_DRAINING */
	if (unlikely(pool->cpu != smp_processor_id() &&
		     !(pool->flags & POOL_BH_DRAINING))) {
		irq_work_queue_on(bh_pool_irq_work(pool), pool->cpu);
		return;
	}
#endif
	if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
		raise_softirq_irqoff(HI_SOFTIRQ);
	else
		raise_softirq_irqoff(TASKLET_SOFTIRQ);
}

/**
 * kick_pool - wake up an idle worker if necessary
 * @pool: pool to kick
 *
 * @pool may have pending work items. Wake up worker if necessary. Returns
 * whether a worker was woken up.
 */
static bool kick_pool(struct worker_pool *pool)
{
	struct worker *worker = first_idle_worker(pool);
	struct task_struct *p;

	lockdep_assert_held(&pool->lock);

	if (!need_more_worker(pool) || !worker)
		return false;

	if (pool->flags & POOL_BH) {
		kick_bh_pool(pool);
		return true;
	}

	p = worker->task;

#ifdef CONFIG_SMP
	/*
	 * Idle @worker is about to execute @work and waking up provides an
	 * opportunity to migrate @worker at a lower cost by setting the task's
	 * wake_cpu field. Let's see if we want to move @worker to improve
	 * execution locality.
	 *
	 * We're waking the worker that went idle the latest and there's some
	 * chance that @worker is marked idle but hasn't gone off CPU yet. If
	 * so, setting the wake_cpu won't do anything. As this is a best-effort
	 * optimization and the race window is narrow, let's leave as-is for
	 * now. If this becomes pronounced, we can skip over workers which are
	 * still on cpu when picking an idle worker.
	 *
	 * If @pool has non-strict affinity, @worker might have ended up outside
	 * its affinity scope. Repatriate.
	 */
	if (!pool->attrs->affn_strict &&
	    !cpumask_test_cpu(p->wake_cpu, pool->attrs->__pod_cpumask)) {
		struct work_struct *work = list_first_entry(&pool->worklist,
						struct work_struct, entry);
		int wake_cpu = cpumask_any_and_distribute(pool->attrs->__pod_cpumask,
							  cpu_online_mask);
		if (wake_cpu < nr_cpu_ids) {
			p->wake_cpu = wake_cpu;
			get_work_pwq(work)->stats[PWQ_STAT_REPATRIATED]++;
		}
	}
#endif
	wake_up_process(p);
	return true;
}

#ifdef CONFIG_WQ_CPU_INTENSIVE_REPORT

/*
 * Concurrency-managed per-cpu work items that hog CPU for longer than
 * wq_cpu_intensive_thresh_us trigger the automatic CPU_INTENSIVE mechanism,
 * which prevents them from stalling other concurrency-managed work items. If a
 * work function keeps triggering this mechanism, it's likely that the work item
 * should be using an unbound workqueue instead.
 *
 * wq_cpu_intensive_report() tracks work functions which trigger such conditions
 * and report them so that they can be examined and converted to use unbound
 * workqueues as appropriate. To avoid flooding the console, each violating work
 * function is tracked and reported with exponential backoff.
 */
#define WCI_MAX_ENTS 128

struct wci_ent {
	work_func_t		func;
	atomic64_t		cnt;
	struct hlist_node	hash_node;
};

static struct wci_ent wci_ents[WCI_MAX_ENTS];
static int wci_nr_ents;
static DEFINE_RAW_SPINLOCK(wci_lock);
static DEFINE_HASHTABLE(wci_hash, ilog2(WCI_MAX_ENTS));

static struct wci_ent *wci_find_ent(work_func_t func)
{
	struct wci_ent *ent;

	hash_for_each_possible_rcu(wci_hash, ent, hash_node,
				   (unsigned long)func) {
		if (ent->func == func)
			return ent;
	}
	return NULL;
}

static void wq_cpu_intensive_report(work_func_t func)
{
	struct wci_ent *ent;

restart:
	ent = wci_find_ent(func);
	if (ent) {
		u64 cnt;

		/*
		 * Start reporting from the warning_thresh and back off
		 * exponentially.
		 */
		cnt = atomic64_inc_return_relaxed(&ent->cnt);
		if (wq_cpu_intensive_warning_thresh &&
		    cnt >= wq_cpu_intensive_warning_thresh &&
		    is_power_of_2(cnt + 1 - wq_cpu_intensive_warning_thresh))
			printk_deferred(KERN_WARNING "workqueue: %ps hogged CPU for >%luus %llu times, consider switching to WQ_UNBOUND\n",
					ent->func, wq_cpu_intensive_thresh_us,
					atomic64_read(&ent->cnt));
		return;
	}

	/*
	 * @func is a new violation. Allocate a new entry for it. If wcn_ents[]
	 * is exhausted, something went really wrong and we probably made enough
	 * noise already.
	 */
	if (wci_nr_ents >= WCI_MAX_ENTS)
		return;

	raw_spin_lock(&wci_lock);

	if (wci_nr_ents >= WCI_MAX_ENTS) {
		raw_spin_unlock(&wci_lock);
		return;
	}

	if (wci_find_ent(func)) {
		raw_spin_unlock(&wci_lock);
		goto restart;
	}

	ent = &wci_ents[wci_nr_ents++];
	ent->func = func;
	atomic64_set(&ent->cnt, 0);
	hash_add_rcu(wci_hash, &ent->hash_node, (unsigned long)func);

	raw_spin_unlock(&wci_lock);

	goto restart;
}

#else	/* CONFIG_WQ_CPU_INTENSIVE_REPORT */
static void wq_cpu_intensive_report(work_func_t func) {}
#endif	/* CONFIG_WQ_CPU_INTENSIVE_REPORT */

/**
 * wq_worker_running - a worker is running again
 * @task: task waking up
 *
 * This function is called when a worker returns from schedule()
 */
void wq_worker_running(struct task_struct *task)
{
	struct worker *worker = kthread_data(task);

	if (!READ_ONCE(worker->sleeping))
		return;

	/*
	 * If preempted by unbind_workers() between the WORKER_NOT_RUNNING check
	 * and the nr_running increment below, we may ruin the nr_running reset
	 * and leave with an unexpected pool->nr_running == 1 on the newly unbound
	 * pool. Protect against such race.
	 */
	preempt_disable();
	if (!(worker->flags & WORKER_NOT_RUNNING))
		worker->pool->nr_running++;
	preempt_enable();

	/*
	 * CPU intensive auto-detection cares about how long a work item hogged
	 * CPU without sleeping. Reset the starting timestamp on wakeup.
	 */
	worker->current_at = worker->task->se.sum_exec_runtime;

	WRITE_ONCE(worker->sleeping, 0);
}

/**
 * wq_worker_sleeping - a worker is going to sleep
 * @task: task going to sleep
 *
 * This function is called from schedule() when a busy worker is
 * going to sleep.
 */
void wq_worker_sleeping(struct task_struct *task)
{
	struct worker *worker = kthread_data(task);
	struct worker_pool *pool;

	/*
	 * Rescuers, which may not have all the fields set up like normal
	 * workers, also reach here, let's not access anything before
	 * checking NOT_RUNNING.
	 */
	if (worker->flags & WORKER_NOT_RUNNING)
		return;

	pool = worker->pool;

	/* Return if preempted before wq_worker_running() was reached */
	if (READ_ONCE(worker->sleeping))
		return;

	WRITE_ONCE(worker->sleeping, 1);
	raw_spin_lock_irq(&pool->lock);

	/*
	 * Recheck in case unbind_workers() preempted us. We don't
	 * want to decrement nr_running after the worker is unbound
	 * and nr_running has been reset.
	 */
	if (worker->flags & WORKER_NOT_RUNNING) {
		raw_spin_unlock_irq(&pool->lock);
		return;
	}

	pool->nr_running--;
	if (kick_pool(pool))
		worker->current_pwq->stats[PWQ_STAT_CM_WAKEUP]++;

	raw_spin_unlock_irq(&pool->lock);
}

/**
 * wq_worker_tick - a scheduler tick occurred while a kworker is running
 * @task: task currently running
 *
 * Called from sched_tick(). We're in the IRQ context and the current
 * worker's fields which follow the 'K' locking rule can be accessed safely.
 */
void wq_worker_tick(struct task_struct *task)
{
	struct worker *worker = kthread_data(task);
	struct pool_workqueue *pwq = worker->current_pwq;
	struct worker_pool *pool = worker->pool;

	if (!pwq)
		return;

	pwq->stats[PWQ_STAT_CPU_TIME] += TICK_USEC;

	if (!wq_cpu_intensive_thresh_us)
		return;

	/*
	 * If the current worker is concurrency managed and hogged the CPU for
	 * longer than wq_cpu_intensive_thresh_us, it's automatically marked
	 * CPU_INTENSIVE to avoid stalling other concurrency-managed work items.
	 *
	 * Set @worker->sleeping means that @worker is in the process of
	 * switching out voluntarily and won't be contributing to
	 * @pool->nr_running until it wakes up. As wq_worker_sleeping() also
	 * decrements ->nr_running, setting CPU_INTENSIVE here can lead to
	 * double decrements. The task is releasing the CPU anyway. Let's skip.
	 * We probably want to make this prettier in the future.
	 */
	if ((worker->flags & WORKER_NOT_RUNNING) || READ_ONCE(worker->sleeping) ||
	    worker->task->se.sum_exec_runtime - worker->current_at <
	    wq_cpu_intensive_thresh_us * NSEC_PER_USEC)
		return;

	raw_spin_lock(&pool->lock);

	worker_set_flags(worker, WORKER_CPU_INTENSIVE);
	wq_cpu_intensive_report(worker->current_func);
	pwq->stats[PWQ_STAT_CPU_INTENSIVE]++;

	if (kick_pool(pool))
		pwq->stats[PWQ_STAT_CM_WAKEUP]++;

	raw_spin_unlock(&pool->lock);
}

/**
 * wq_worker_last_func - retrieve worker's last work function
 * @task: Task to retrieve last work function of.
 *
 * Determine the last function a worker executed. This is called from
 * the scheduler to get a worker's last known identity.
 *
 * CONTEXT:
 * raw_spin_lock_irq(rq->lock)
 *
 * This function is called during schedule() when a kworker is going
 * to sleep. It's used by psi to identify aggregation workers during
 * dequeuing, to allow periodic aggregation to shut-off when that
 * worker is the last task in the system or cgroup to go to sleep.
 *
 * As this function doesn't involve any workqueue-related locking, it
 * only returns stable values when called from inside the scheduler's
 * queuing and dequeuing paths, when @task, which must be a kworker,
 * is guaranteed to not be processing any works.
 *
 * Return:
 * The last work function %current executed as a worker, NULL if it
 * hasn't executed any work yet.
 */
work_func_t wq_worker_last_func(struct task_struct *task)
{
	struct worker *worker = kthread_data(task);

	return worker->last_func;
}

/**
 * wq_node_nr_active - Determine wq_node_nr_active to use
 * @wq: workqueue of interest
 * @node: NUMA node, can be %NUMA_NO_NODE
 *
 * Determine wq_node_nr_active to use for @wq on @node. Returns:
 *
 * - %NULL for per-cpu workqueues as they don't need to use shared nr_active.
 *
 * - node_nr_active[nr_node_ids] if @node is %NUMA_NO_NODE.
 *
 * - Otherwise, node_nr_active[@node].
 */
static struct wq_node_nr_active *wq_node_nr_active(struct workqueue_struct *wq,
						   int node)
{
	if (!(wq->flags & WQ_UNBOUND))
		return NULL;

	if (node == NUMA_NO_NODE)
		node = nr_node_ids;

	return wq->node_nr_active[node];
}

/**
 * wq_update_node_max_active - Update per-node max_actives to use
 * @wq: workqueue to update
 * @off_cpu: CPU that's going down, -1 if a CPU is not going down
 *
 * Update @wq->node_nr_active[]->max. @wq must be unbound. max_active is
 * distributed among nodes according to the proportions of numbers of online
 * cpus. The result is always between @wq->min_active and max_active.
 */
static void wq_update_node_max_active(struct workqueue_struct *wq, int off_cpu)
{
	struct cpumask *effective = unbound_effective_cpumask(wq);
	int min_active = READ_ONCE(wq->min_active);
	int max_active = READ_ONCE(wq->max_active);
	int total_cpus, node;

	lockdep_assert_held(&wq->mutex);

	if (!wq_topo_initialized)
		return;

	if (off_cpu >= 0 && !cpumask_test_cpu(off_cpu, effective))
		off_cpu = -1;

	total_cpus = cpumask_weight_and(effective, cpu_online_mask);
	if (off_cpu >= 0)
		total_cpus--;

	/* If all CPUs of the wq get offline, use the default values */
	if (unlikely(!total_cpus)) {
		for_each_node(node)
			wq_node_nr_active(wq, node)->max = min_active;

		wq_node_nr_active(wq, NUMA_NO_NODE)->max = max_active;
		return;
	}

	for_each_node(node) {
		int node_cpus;

		node_cpus = cpumask_weight_and(effective, cpumask_of_node(node));
		if (off_cpu >= 0 && cpu_to_node(off_cpu) == node)
			node_cpus--;

		wq_node_nr_active(wq, node)->max =
			clamp(DIV_ROUND_UP(max_active * node_cpus, total_cpus),
			      min_active, max_active);
	}

	wq_node_nr_active(wq, NUMA_NO_NODE)->max = max_active;
}

/**
 * get_pwq - get an extra reference on the specified pool_workqueue
 * @pwq: pool_workqueue to get
 *
 * Obtain an extra reference on @pwq.  The caller should guarantee that
 * @pwq has positive refcnt and be holding the matching pool->lock.
 */
static void get_pwq(struct pool_workqueue *pwq)
{
	lockdep_assert_held(&pwq->pool->lock);
	WARN_ON_ONCE(pwq->refcnt <= 0);
	pwq->refcnt++;
}

/**
 * put_pwq - put a pool_workqueue reference
 * @pwq: pool_workqueue to put
 *
 * Drop a reference of @pwq.  If its refcnt reaches zero, schedule its
 * destruction.  The caller should be holding the matching pool->lock.
 */
static void put_pwq(struct pool_workqueue *pwq)
{
	lockdep_assert_held(&pwq->pool->lock);
	if (likely(--pwq->refcnt))
		return;
	/*
	 * @pwq can't be released under pool->lock, bounce to a dedicated
	 * kthread_worker to avoid A-A deadlocks.
	 */
	kthread_queue_work(pwq_release_worker, &pwq->release_work);
}

/**
 * put_pwq_unlocked - put_pwq() with surrounding pool lock/unlock
 * @pwq: pool_workqueue to put (can be %NULL)
 *
 * put_pwq() with locking.  This function also allows %NULL @pwq.
 */
static void put_pwq_unlocked(struct pool_workqueue *pwq)
{
	if (pwq) {
		/*
		 * As both pwqs and pools are RCU protected, the
		 * following lock operations are safe.
		 */
		raw_spin_lock_irq(&pwq->pool->lock);
		put_pwq(pwq);
		raw_spin_unlock_irq(&pwq->pool->lock);
	}
}

static bool pwq_is_empty(struct pool_workqueue *pwq)
{
	return !pwq->nr_active && list_empty(&pwq->inactive_works);
}

static void __pwq_activate_work(struct pool_workqueue *pwq,
				struct work_struct *work)
{
	unsigned long *wdb = work_data_bits(work);

	WARN_ON_ONCE(!(*wdb & WORK_STRUCT_INACTIVE));
	trace_workqueue_activate_work(work);
	if (list_empty(&pwq->pool->worklist))
		pwq->pool->last_progress_ts = jiffies;
	move_linked_works(work, &pwq->pool->worklist, NULL);
	__clear_bit(WORK_STRUCT_INACTIVE_BIT, wdb);
}

static bool tryinc_node_nr_active(struct wq_node_nr_active *nna)
{
	int max = READ_ONCE(nna->max);
	int old = atomic_read(&nna->nr);

	do {
		if (old >= max)
			return false;
	} while (!atomic_try_cmpxchg_relaxed(&nna->nr, &old, old + 1));

	return true;
}

/**
 * pwq_tryinc_nr_active - Try to increment nr_active for a pwq
 * @pwq: pool_workqueue of interest
 * @fill: max_active may have increased, try to increase concurrency level
 *
 * Try to increment nr_active for @pwq. Returns %true if an nr_active count is
 * successfully obtained. %false otherwise.
 */
static bool pwq_tryinc_nr_active(struct pool_workqueue *pwq, bool fill)
{
	struct workqueue_struct *wq = pwq->wq;
	struct worker_pool *pool = pwq->pool;
	struct wq_node_nr_active *nna = wq_node_nr_active(wq, pool->node);
	bool obtained = false;

	lockdep_assert_held(&pool->lock);

	if (!nna) {
		/* BH or per-cpu workqueue, pwq->nr_active is sufficient */
		obtained = pwq->nr_active < READ_ONCE(wq->max_active);
		goto out;
	}

	if (unlikely(pwq->plugged))
		return false;

	/*
	 * Unbound workqueue uses per-node shared nr_active $nna. If @pwq is
	 * already waiting on $nna, pwq_dec_nr_active() will maintain the
	 * concurrency level. Don't jump the line.
	 *
	 * We need to ignore the pending test after max_active has increased as
	 * pwq_dec_nr_active() can only maintain the concurrency level but not
	 * increase it. This is indicated by @fill.
	 */
	if (!list_empty(&pwq->pending_node) && likely(!fill))
		goto out;

	obtained = tryinc_node_nr_active(nna);
	if (obtained)
		goto out;

	/*
	 * Lockless acquisition failed. Lock, add ourself to $nna->pending_pwqs
	 * and try again. The smp_mb() is paired with the implied memory barrier
	 * of atomic_dec_return() in pwq_dec_nr_active() to ensure that either
	 * we see the decremented $nna->nr or they see non-empty
	 * $nna->pending_pwqs.
	 */
	raw_spin_lock(&nna->lock);

	if (list_empty(&pwq->pending_node))
		list_add_tail(&pwq->pending_node, &nna->pending_pwqs);
	else if (likely(!fill))
		goto out_unlock;

	smp_mb();

	obtained = tryinc_node_nr_active(nna);

	/*
	 * If @fill, @pwq might have already been pending. Being spuriously
	 * pending in cold paths doesn't affect anything. Let's leave it be.
	 */
	if (obtained && likely(!fill))
		list_del_init(&pwq->pending_node);

out_unlock:
	raw_spin_unlock(&nna->lock);
out:
	if (obtained)
		pwq->nr_active++;
	return obtained;
}

/**
 * pwq_activate_first_inactive - Activate the first inactive work item on a pwq
 * @pwq: pool_workqueue of interest
 * @fill: max_active may have increased, try to increase concurrency level
 *
 * Activate the first inactive work item of @pwq if available and allowed by
 * max_active limit.
 *
 * Returns %true if an inactive work item has been activated. %false if no
 * inactive work item is found or max_active limit is reached.
 */
static bool pwq_activate_first_inactive(struct pool_workqueue *pwq, bool fill)
{
	struct work_struct *work =
		list_first_entry_or_null(&pwq->inactive_works,
					 struct work_struct, entry);

	if (work && pwq_tryinc_nr_active(pwq, fill)) {
		__pwq_activate_work(pwq, work);
		return true;
	} else {
		return false;
	}
}

/**
 * unplug_oldest_pwq - unplug the oldest pool_workqueue
 * @wq: workqueue_struct where its oldest pwq is to be unplugged
 *
 * This function should only be called for ordered workqueues where only the
 * oldest pwq is unplugged, the others are plugged to suspend execution to
 * ensure proper work item ordering::
 *
 *    dfl_pwq --------------+     [P] - plugged
 *                          |
 *                          v
 *    pwqs -> A -> B [P] -> C [P] (newest)
 *            |    |        |
 *            1    3        5
 *            |    |        |
 *            2    4        6
 *
 * When the oldest pwq is drained and removed, this function should be called
 * to unplug the next oldest one to start its work item execution. Note that
 * pwq's are linked into wq->pwqs with the oldest first, so the first one in
 * the list is the oldest.
 */
static void unplug_oldest_pwq(struct workqueue_struct *wq)
{
	struct pool_workqueue *pwq;

	lockdep_assert_held(&wq->mutex);

	/* Caller should make sure that pwqs isn't empty before calling */
	pwq = list_first_entry_or_null(&wq->pwqs, struct pool_workqueue,
				       pwqs_node);
	raw_spin_lock_irq(&pwq->pool->lock);
	if (pwq->plugged) {
		pwq->plugged = false;
		if (pwq_activate_first_inactive(pwq, true)) {
			/*
			 * While plugged, queueing skips activation which
			 * includes bumping the nr_active count and adding the
			 * pwq to nna->pending_pwqs if the count can't be
			 * obtained. We need to restore both for the pwq being
			 * unplugged. The first call activates the first
			 * inactive work item and the second, if there are more
			 * inactive, puts the pwq on pending_pwqs.
			 */
			pwq_activate_first_inactive(pwq, false);

			kick_pool(pwq->pool);
		}
	}
	raw_spin_unlock_irq(&pwq->pool->lock);
}

/**
 * node_activate_pending_pwq - Activate a pending pwq on a wq_node_nr_active
 * @nna: wq_node_nr_active to activate a pending pwq for
 * @caller_pool: worker_pool the caller is locking
 *
 * Activate a pwq in @nna->pending_pwqs. Called with @caller_pool locked.
 * @caller_pool may be unlocked and relocked to lock other worker_pools.
 */
static void node_activate_pending_pwq(struct wq_node_nr_active *nna,
				      struct worker_pool *caller_pool)
{
	struct worker_pool *locked_pool = caller_pool;
	struct pool_workqueue *pwq;
	struct work_struct *work;

	lockdep_assert_held(&caller_pool->lock);

	raw_spin_lock(&nna->lock);
retry:
	pwq = list_first_entry_or_null(&nna->pending_pwqs,
				       struct pool_workqueue, pending_node);
	if (!pwq)
		goto out_unlock;

	/*
	 * If @pwq is for a different pool than @locked_pool, we need to lock
	 * @pwq->pool->lock. Let's trylock first. If unsuccessful, do the unlock
	 * / lock dance. For that, we also need to release @nna->lock as it's
	 * nested inside pool locks.
	 */
	if (pwq->pool != locked_pool) {
		raw_spin_unlock(&locked_pool->lock);
		locked_pool = pwq->pool;
		if (!raw_spin_trylock(&locked_pool->lock)) {
			raw_spin_unlock(&nna->lock);
			raw_spin_lock(&locked_pool->lock);
			raw_spin_lock(&nna->lock);
			goto retry;
		}
	}

	/*
	 * $pwq may not have any inactive work items due to e.g. cancellations.
	 * Drop it from pending_pwqs and see if there's another one.
	 */
	work = list_first_entry_or_null(&pwq->inactive_works,
					struct work_struct, entry);
	if (!work) {
		list_del_init(&pwq->pending_node);
		goto retry;
	}

	/*
	 * Acquire an nr_active count and activate the inactive work item. If
	 * $pwq still has inactive work items, rotate it to the end of the
	 * pending_pwqs so that we round-robin through them. This means that
	 * inactive work items are not activated in queueing order which is fine
	 * given that there has never been any ordering across different pwqs.
	 */
	if (likely(tryinc_node_nr_active(nna))) {
		pwq->nr_active++;
		__pwq_activate_work(pwq, work);

		if (list_empty(&pwq->inactive_works))
			list_del_init(&pwq->pending_node);
		else
			list_move_tail(&pwq->pending_node, &nna->pending_pwqs);

		/* if activating a foreign pool, make sure it's running */
		if (pwq->pool != caller_pool)
			kick_pool(pwq->pool);
	}

out_unlock:
	raw_spin_unlock(&nna->lock);
	if (locked_pool != caller_pool) {
		raw_spin_unlock(&locked_pool->lock);
		raw_spin_lock(&caller_pool->lock);
	}
}

/**
 * pwq_dec_nr_active - Retire an active count
 * @pwq: pool_workqueue of interest
 *
 * Decrement @pwq's nr_active and try to activate the first inactive work item.
 * For unbound workqueues, this function may temporarily drop @pwq->pool->lock.
 */
static void pwq_dec_nr_active(struct pool_workqueue *pwq)
{
	struct worker_pool *pool = pwq->pool;
	struct wq_node_nr_active *nna = wq_node_nr_active(pwq->wq, pool->node);

	lockdep_assert_held(&pool->lock);

	/*
	 * @pwq->nr_active should be decremented for both percpu and unbound
	 * workqueues.
	 */
	pwq->nr_active--;

	/*
	 * For a percpu workqueue, it's simple. Just need to kick the first
	 * inactive work item on @pwq itself.
	 */
	if (!nna) {
		pwq_activate_first_inactive(pwq, false);
		return;
	}

	/*
	 * If @pwq is for an unbound workqueue, it's more complicated because
	 * multiple pwqs and pools may be sharing the nr_active count. When a
	 * pwq needs to wait for an nr_active count, it puts itself on
	 * $nna->pending_pwqs. The following atomic_dec_return()'s implied
	 * memory barrier is paired with smp_mb() in pwq_tryinc_nr_active() to
	 * guarantee that either we see non-empty pending_pwqs or they see
	 * decremented $nna->nr.
	 *
	 * $nna->max may change as CPUs come online/offline and @pwq->wq's
	 * max_active gets updated. However, it is guaranteed to be equal to or
	 * larger than @pwq->wq->min_active which is above zero unless freezing.
	 * This maintains the forward progress guarantee.
	 */
	if (atomic_dec_return(&nna->nr) >= READ_ONCE(nna->max))
		return;

	if (!list_empty(&nna->pending_pwqs))
		node_activate_pending_pwq(nna, pool);
}

/**
 * pwq_dec_nr_in_flight - decrement pwq's nr_in_flight
 * @pwq: pwq of interest
 * @work_data: work_data of work which left the queue
 *
 * A work either has completed or is removed from pending queue,
 * decrement nr_in_flight of its pwq and handle workqueue flushing.
 *
 * NOTE:
 * For unbound workqueues, this function may temporarily drop @pwq->pool->lock
 * and thus should be called after all other state updates for the in-flight
 * work item is complete.
 *
 * CONTEXT:
 * raw_spin_lock_irq(pool->lock).
 */
static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, unsigned long work_data)
{
	int color = get_work_color(work_data);

	if (!(work_data & WORK_STRUCT_INACTIVE))
		pwq_dec_nr_active(pwq);

	pwq->nr_in_flight[color]--;

	/* is flush in progress and are we at the flushing tip? */
	if (likely(pwq->flush_color != color))
		goto out_put;

	/* are there still in-flight works? */
	if (pwq->nr_in_flight[color])
		goto out_put;

	/* this pwq is done, clear flush_color */
	pwq->flush_color = -1;

	/*
	 * If this was the last pwq, wake up the first flusher.  It
	 * will handle the rest.
	 */
	if (atomic_dec_and_test(&pwq->wq->nr_pwqs_to_flush))
		complete(&pwq->wq->first_flusher->done);
out_put:
	put_pwq(pwq);
}

/**
 * try_to_grab_pending - steal work item from worklist and disable irq
 * @work: work item to steal
 * @cflags: %WORK_CANCEL_ flags
 * @irq_flags: place to store irq state
 *
 * Try to grab PENDING bit of @work.  This function can handle @work in any
 * stable state - idle, on timer or on worklist.
 *
 * Return:
 *
 *  ========	================================================================
 *  1		if @work was pending and we successfully stole PENDING
 *  0		if @work was idle and we claimed PENDING
 *  -EAGAIN	if PENDING couldn't be grabbed at the moment, safe to busy-retry
 *  ========	================================================================
 *
 * Note:
 * On >= 0 return, the caller owns @work's PENDING bit.  To avoid getting
 * interrupted while holding PENDING and @work off queue, irq must be
 * disabled on entry.  This, combined with delayed_work->timer being
 * irqsafe, ensures that we return -EAGAIN for finite short period of time.
 *
 * On successful return, >= 0, irq is disabled and the caller is
 * responsible for releasing it using local_irq_restore(*@irq_flags).
 *
 * This function is safe to call from any context including IRQ handler.
 */
static int try_to_grab_pending(struct work_struct *work, u32 cflags,
			       unsigned long *irq_flags)
{
	struct worker_pool *pool;
	struct pool_workqueue *pwq;

	local_irq_save(*irq_flags);

	/* try to steal the timer if it exists */
	if (cflags & WORK_CANCEL_DELAYED) {
		struct delayed_work *dwork = to_delayed_work(work);

		/*
		 * dwork->timer is irqsafe.  If timer_delete() fails, it's
		 * guaranteed that the timer is not queued anywhere and not
		 * running on the local CPU.
		 */
		if (likely(timer_delete(&dwork->timer)))
			return 1;
	}

	/* try to claim PENDING the normal way */
	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
		return 0;

	rcu_read_lock();
	/*
	 * The queueing is in progress, or it is already queued. Try to
	 * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
	 */
	pool = get_work_pool(work);
	if (!pool)
		goto fail;

	raw_spin_lock(&pool->lock);
	/*
	 * work->data is guaranteed to point to pwq only while the work
	 * item is queued on pwq->wq, and both updating work->data to point
	 * to pwq on queueing and to pool on dequeueing are done under
	 * pwq->pool->lock.  This in turn guarantees that, if work->data
	 * points to pwq which is associated with a locked pool, the work
	 * item is currently queued on that pool.
	 */
	pwq = get_work_pwq(work);
	if (pwq && pwq->pool == pool) {
		unsigned long work_data = *work_data_bits(work);

		debug_work_deactivate(work);

		/*
		 * A cancelable inactive work item must be in the
		 * pwq->inactive_works since a queued barrier can't be
		 * canceled (see the comments in insert_wq_barrier()).
		 *
		 * An inactive work item cannot be deleted directly because
		 * it might have linked barrier work items which, if left
		 * on the inactive_works list, will confuse pwq->nr_active
		 * management later on and cause stall.  Move the linked
		 * barrier work items to the worklist when deleting the grabbed
		 * item. Also keep WORK_STRUCT_INACTIVE in work_data, so that
		 * it doesn't participate in nr_active management in later
		 * pwq_dec_nr_in_flight().
		 */
		if (work_data & WORK_STRUCT_INACTIVE)
			move_linked_works(work, &pwq->pool->worklist, NULL);

		list_del_init(&work->entry);

		/*
		 * work->data points to pwq iff queued. Let's point to pool. As
		 * this destroys work->data needed by the next step, stash it.
		 */
		set_work_pool_and_keep_pending(work, pool->id,
					       pool_offq_flags(pool));

		/* must be the last step, see the function comment */
		pwq_dec_nr_in_flight(pwq, work_data);

		raw_spin_unlock(&pool->lock);
		rcu_read_unlock();
		return 1;
	}
	raw_spin_unlock(&pool->lock);
fail:
	rcu_read_unlock();
	local_irq_restore(*irq_flags);
	return -EAGAIN;
}

/**
 * work_grab_pending - steal work item from worklist and disable irq
 * @work: work item to steal
 * @cflags: %WORK_CANCEL_ flags
 * @irq_flags: place to store IRQ state
 *
 * Grab PENDING bit of @work. @work can be in any stable state - idle, on timer
 * or on worklist.
 *
 * Can be called from any context. IRQ is disabled on return with IRQ state
 * stored in *@irq_flags. The caller is responsible for re-enabling it using
 * local_irq_restore().
 *
 * Returns %true if @work was pending. %false if idle.
 */
static bool work_grab_pending(struct work_struct *work, u32 cflags,
			      unsigned long *irq_flags)
{
	int ret;

	while (true) {
		ret = try_to_grab_pending(work, cflags, irq_flags);
		if (ret >= 0)
			return ret;
		cpu_relax();
	}
}

/**
 * insert_work - insert a work into a pool
 * @pwq: pwq @work belongs to
 * @work: work to insert
 * @head: insertion point
 * @extra_flags: extra WORK_STRUCT_* flags to set
 *
 * Insert @work which belongs to @pwq after @head.  @extra_flags is or'd to
 * work_struct flags.
 *
 * CONTEXT:
 * raw_spin_lock_irq(pool->lock).
 */
static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
			struct list_head *head, unsigned int extra_flags)
{
	debug_work_activate(work);

	/* record the work call stack in order to print it in KASAN reports */
	kasan_record_aux_stack(work);

	/* we own @work, set data and link */
	set_work_pwq(work, pwq, extra_flags);
	list_add_tail(&work->entry, head);
	get_pwq(pwq);
}

/*
 * Test whether @work is being queued from another work executing on the
 * same workqueue.
 */
static bool is_chained_work(struct workqueue_struct *wq)
{
	struct worker *worker;

	worker = current_wq_worker();
	/*
	 * Return %true iff I'm a worker executing a work item on @wq.  If
	 * I'm @worker, it's safe to dereference it without locking.
	 */
	return worker && worker->current_pwq->wq == wq;
}

/*
 * When queueing an unbound work item to a wq, prefer local CPU if allowed
 * by wq_unbound_cpumask.  Otherwise, round robin among the allowed ones to
 * avoid perturbing sensitive tasks.
 */
static int wq_select_unbound_cpu(int cpu)
{
	int new_cpu;

	if (likely(!wq_debug_force_rr_cpu)) {
		if (cpumask_test_cpu(cpu, wq_unbound_cpumask))
			return cpu;
	} else {
		pr_warn_once("workqueue: round-robin CPU selection forced, expect performance impact\n");
	}

	new_cpu = __this_cpu_read(wq_rr_cpu_last);
	new_cpu = cpumask_next_and_wrap(new_cpu, wq_unbound_cpumask, cpu_online_mask);
	if (unlikely(new_cpu >= nr_cpu_ids))
		return cpu;
	__this_cpu_write(wq_rr_cpu_last, new_cpu);

	return new_cpu;
}

static void __queue_work(int cpu, struct workqueue_struct *wq,
			 struct work_struct *work)
{
	struct pool_workqueue *pwq;
	struct worker_pool *last_pool, *pool;
	unsigned int work_flags;
	unsigned int req_cpu = cpu;

	/*
	 * While a work item is PENDING && off queue, a task trying to
	 * steal the PENDING will busy-loop waiting for it to either get
	 * queued or lose PENDING.  Grabbing PENDING and queueing should
	 * happen with IRQ disabled.
	 */
	lockdep_assert_irqs_disabled();

	/*
	 * For a draining wq, only works from the same workqueue are
	 * allowed. The __WQ_DESTROYING helps to spot the issue that
	 * queues a new work item to a wq after destroy_workqueue(wq).
	 */
	if (unlikely(wq->flags & (__WQ_DESTROYING | __WQ_DRAINING) &&
		     WARN_ONCE(!is_chained_work(wq), "workqueue: cannot queue %ps on wq %s\n",
			       work->func, wq->name))) {
		struct work_offq_data offqd;

		/*
		 * State on entry: PENDING is set, work is off-queue (no
		 * insert_work() has run).
		 *
		 * Returning without clearing PENDING would leave the work
		 * in a weird state (PENDING=1, PWQ=0, entry empty)
		 */
		work_offqd_unpack(&offqd, *work_data_bits(work));
		set_work_pool_and_clear_pending(work, offqd.pool_id,
						work_offqd_pack_flags(&offqd));
		return;
	}
	rcu_read_lock();
retry:
	/* pwq which will be used unless @work is executing elsewhere */
	if (req_cpu == WORK_CPU_UNBOUND) {
		if (wq->flags & WQ_UNBOUND)
			cpu = wq_select_unbound_cpu(raw_smp_processor_id());
		else
			cpu = raw_smp_processor_id();
	}

	pwq = rcu_dereference(*per_cpu_ptr(wq->cpu_pwq, cpu));
	pool = pwq->pool;

	/*
	 * If @work was previously on a different pool, it might still be
	 * running there, in which case the work needs to be queued on that
	 * pool to guarantee non-reentrancy.
	 *
	 * For ordered workqueue, work items must be queued on the newest pwq
	 * for accurate order management.  Guaranteed order also guarantees
	 * non-reentrancy.  See the comments above unplug_oldest_pwq().
	 */
	last_pool = get_work_pool(work);
	if (last_pool && last_pool != pool && !(wq->flags & __WQ_ORDERED)) {
		struct worker *worker;

		raw_spin_lock(&last_pool->lock);

		worker = find_worker_executing_work(last_pool, work);

		if (worker && worker->current_pwq->wq == wq) {
			pwq = worker->current_pwq;
			pool = pwq->pool;
			WARN_ON_ONCE(pool != last_pool);
		} else {
			/* meh... not running there, queue here */
			raw_spin_unlock(&last_pool->lock);
			raw_spin_lock(&pool->lock);
		}
	} else {
		raw_spin_lock(&pool->lock);
	}

	/*
	 * pwq is determined and locked. For unbound pools, we could have raced
	 * with pwq release and it could already be dead. If its refcnt is zero,
	 * repeat pwq selection. Note that unbound pwqs never die without
	 * another pwq replacing it in cpu_pwq or while work items are executing
	 * on it, so the retrying is guaranteed to make forward-progress.
	 */
	if (unlikely(!pwq->refcnt)) {
		if (wq->flags & WQ_UNBOUND) {
			raw_spin_unlock(&pool->lock);
			cpu_relax();
			goto retry;
		}
		/* oops */
		WARN_ONCE(true, "workqueue: per-cpu pwq for %s on cpu%d has 0 refcnt",
			  wq->name, cpu);
	}

	/* pwq determined, queue */
	trace_workqueue_queue_work(req_cpu, pwq, work);

	if (WARN_ON(!list_empty(&work->entry)))
		goto out;

	pwq->nr_in_flight[pwq->work_color]++;
	work_flags = work_color_to_flags(pwq->work_color);

	/*
	 * Limit the number of concurrently active work items to max_active.
	 * @work must also queue behind existing inactive work items to maintain
	 * ordering when max_active changes. See wq_adjust_max_active().
	 */
	if (list_empty(&pwq->inactive_works) && pwq_tryinc_nr_active(pwq, false)) {
		if (list_empty(&pool->worklist))
			pool->last_progress_ts = jiffies;

		trace_workqueue_activate_work(work);
		insert_work(pwq, work, &pool->worklist, work_flags);
		kick_pool(pool);
	} else {
		work_flags |= WORK_STRUCT_INACTIVE;
		insert_work(pwq, work, &pwq->inactive_works, work_flags);
	}

out:
	raw_spin_unlock(&pool->lock);
	rcu_read_unlock();
}

static bool clear_pending_if_disabled(struct work_struct *work)
{
	unsigned long data = *work_data_bits(work);
	struct work_offq_data offqd;

	if (likely((data & WORK_STRUCT_PWQ) ||
		   !(data & WORK_OFFQ_DISABLE_MASK)))
		return false;

	work_offqd_unpack(&offqd, data);
	set_work_pool_and_clear_pending(work, offqd.pool_id,
					work_offqd_pack_flags(&offqd));
	return true;
}

/**
 * queue_work_on - queue work on specific cpu
 * @cpu: CPU number to execute work on
 * @wq: workqueue to use
 * @work: work to queue
 *
 * We queue the work to a specific CPU, the caller must ensure it
 * can't go away.  Callers that fail to ensure that the specified
 * CPU cannot go away will execute on a randomly chosen CPU.
 * But note well that callers specifying a CPU that never has been
 * online will get a splat.
 *
 * Return: %false if @work was already on a queue, %true otherwise.
 */
bool queue_work_on(int cpu, struct workqueue_struct *wq,
		   struct work_struct *work)
{
	bool ret = false;
	unsigned long irq_flags;

	local_irq_save(irq_flags);

	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
	    !clear_pending_if_disabled(work)) {
		__queue_work(cpu, wq, work);
		ret = true;
	}

	local_irq_restore(irq_flags);
	return ret;
}
EXPORT_SYMBOL(queue_work_on);

/**
 * select_numa_node_cpu - Select a CPU based on NUMA node
 * @node: NUMA node ID that we want to select a CPU from
 *
 * This function will attempt to find a "random" cpu available on a given
 * node. If there are no CPUs available on the given node it will return
 * WORK_CPU_UNBOUND indicating that we should just schedule to any
 * available CPU if we need to schedule this work.
 */
static int select_numa_node_cpu(int node)
{
	int cpu;

	/* Delay binding to CPU if node is not valid or online */
	if (node < 0 || node >= MAX_NUMNODES || !node_online(node))
		return WORK_CPU_UNBOUND;

	/* Use local node/cpu if we are already there */
	cpu = raw_smp_processor_id();
	if (node == cpu_to_node(cpu))
		return cpu;

	/* Use "random" otherwise know as "first" online CPU of node */
	cpu = cpumask_any_and(cpumask_of_node(node), cpu_online_mask);

	/* If CPU is valid return that, otherwise just defer */
	return cpu < nr_cpu_ids ? cpu : WORK_CPU_UNBOUND;
}

/**
 * queue_work_node - queue work on a "random" cpu for a given NUMA node
 * @node: NUMA node that we are targeting the work for
 * @wq: workqueue to use
 * @work: work to queue
 *
 * We queue the work to a "random" CPU within a given NUMA node. The basic
 * idea here is to provide a way to somehow associate work with a given
 * NUMA node.
 *
 * This function will only make a best effort attempt at getting this onto
 * the right NUMA node. If no node is requested or the requested node is
 * offline then we just fall back to standard queue_work behavior.
 *
 * Currently the "random" CPU ends up being the first available CPU in the
 * intersection of cpu_online_mask and the cpumask of the node, unless we
 * are running on the node. In that case we just use the current CPU.
 *
 * Return: %false if @work was already on a queue, %true otherwise.
 */
bool queue_work_node(int node, struct workqueue_struct *wq,
		     struct work_struct *work)
{
	unsigned long irq_flags;
	bool ret = false;

	/*
	 * This current implementation is specific to unbound workqueues.
	 * Specifically we only return the first available CPU for a given
	 * node instead of cycling through individual CPUs within the node.
	 *
	 * If this is used with a per-cpu workqueue then the logic in
	 * workqueue_select_cpu_near would need to be updated to allow for
	 * some round robin type logic.
	 */
	WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND));

	local_irq_save(irq_flags);

	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
	    !clear_pending_if_disabled(work)) {
		int cpu = select_numa_node_cpu(node);

		__queue_work(cpu, wq, work);
		ret = true;
	}

	local_irq_restore(irq_flags);
	return ret;
}
EXPORT_SYMBOL_GPL(queue_work_node);

void delayed_work_timer_fn(struct timer_list *t)
{
	struct delayed_work *dwork = timer_container_of(dwork, t, timer);

	/* should have been called from irqsafe timer with irq already off */
	__queue_work(dwork->cpu, dwork->wq, &dwork->work);
}
EXPORT_SYMBOL(delayed_work_timer_fn);

static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
				struct delayed_work *dwork, unsigned long delay)
{
	struct timer_list *timer = &dwork->timer;
	struct work_struct *work = &dwork->work;

	WARN_ON_ONCE(timer->function != delayed_work_timer_fn);
	WARN_ON_ONCE(timer_pending(timer));
	WARN_ON_ONCE(!list_empty(&work->entry));

	/*
	 * If @delay is 0, queue @dwork->work immediately.  This is for
	 * both optimization and correctness.  The earliest @timer can
	 * expire is on the closest next tick and delayed_work users depend
	 * on that there's no such delay when @delay is 0.
	 */
	if (!delay) {
		__queue_work(cpu, wq, &dwork->work);
		return;
	}

	WARN_ON_ONCE(cpu != WORK_CPU_UNBOUND && !cpu_online(cpu));
	dwork->wq = wq;
	dwork->cpu = cpu;
	timer->expires = jiffies + delay;

	if (housekeeping_enabled(HK_TYPE_TIMER)) {
		/* If the current cpu is a housekeeping cpu, use it. */
		cpu = smp_processor_id();
		if (!housekeeping_test_cpu(cpu, HK_TYPE_TIMER))
			cpu = housekeeping_any_cpu(HK_TYPE_TIMER);
		add_timer_on(timer, cpu);
	} else {
		if (likely(cpu == WORK_CPU_UNBOUND))
			add_timer_global(timer);
		else
			add_timer_on(timer, cpu);
	}
}

/**
 * queue_delayed_work_on - queue work on specific CPU after delay
 * @cpu: CPU number to execute work on
 * @wq: workqueue to use
 * @dwork: work to queue
 * @delay: number of jiffies to wait before queueing
 *
 * We queue the delayed_work to a specific CPU, for non-zero delays the
 * caller must ensure it is online and can't go away. Callers that fail
 * to ensure this, may get @dwork->timer queued to an offlined CPU and
 * this will prevent queueing of @dwork->work unless the offlined CPU
 * becomes online again.
 *
 * Return: %false if @work was already on a queue, %true otherwise.  If
 * @delay is zero and @dwork is idle, it will be scheduled for immediate
 * execution.
 */
bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
			   struct delayed_work *dwork, unsigned long delay)
{
	struct work_struct *work = &dwork->work;
	bool ret = false;
	unsigned long irq_flags;

	/* read the comment in __queue_work() */
	local_irq_save(irq_flags);

	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
	    !clear_pending_if_disabled(work)) {
		__queue_delayed_work(cpu, wq, dwork, delay);
		ret = true;
	}

	local_irq_restore(irq_flags);
	return ret;
}
EXPORT_SYMBOL(queue_delayed_work_on);

/**
 * mod_delayed_work_on - modify delay of or queue a delayed work on specific CPU
 * @cpu: CPU number to execute work on
 * @wq: workqueue to use
 * @dwork: work to queue
 * @delay: number of jiffies to wait before queueing
 *
 * If @dwork is idle, equivalent to queue_delayed_work_on(); otherwise,
 * modify @dwork's timer so that it expires after @delay.  If @delay is
 * zero, @work is guaranteed to be scheduled immediately regardless of its
 * current state.
 *
 * Return: %false if @dwork was idle and queued, %true if @dwork was
 * pending and its timer was modified.
 *
 * This function is safe to call from any context including IRQ handler.
 * See try_to_grab_pending() for details.
 */
bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,
			 struct delayed_work *dwork, unsigned long delay)
{
	unsigned long irq_flags;
	bool ret;

	ret = work_grab_pending(&dwork->work, WORK_CANCEL_DELAYED, &irq_flags);

	if (!clear_pending_if_disabled(&dwork->work))
		__queue_delayed_work(cpu, wq, dwork, delay);

	local_irq_restore(irq_flags);
	return ret;
}
EXPORT_SYMBOL_GPL(mod_delayed_work_on);

static void rcu_work_rcufn(struct rcu_head *rcu)
{
	struct rcu_work *rwork = container_of(rcu, struct rcu_work, rcu);

	/* read the comment in __queue_work() */
	local_irq_disable();
	__queue_work(WORK_CPU_UNBOUND, rwork->wq, &rwork->work);
	local_irq_enable();
}

/**
 * queue_rcu_work - queue work after a RCU grace period
 * @wq: workqueue to use
 * @rwork: work to queue
 *
 * Return: %false if @rwork was already pending, %true otherwise.  Note
 * that a full RCU grace period is guaranteed only after a %true return.
 * While @rwork is guaranteed to be executed after a %false return, the
 * execution may happen before a full RCU grace period has passed.
 */
bool queue_rcu_work(struct workqueue_struct *wq, struct rcu_work *rwork)
{
	struct work_struct *work = &rwork->work;

	/*
	 * rcu_work can't be canceled or disabled. Warn if the user reached
	 * inside @rwork and disabled the inner work.
	 */
	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)) &&
	    !WARN_ON_ONCE(clear_pending_if_disabled(work))) {
		rwork->wq = wq;
		call_rcu_hurry(&rwork->rcu, rcu_work_rcufn);
		return true;
	}

	return false;
}
EXPORT_SYMBOL(queue_rcu_work);

static struct worker *alloc_worker(int node)
{
	struct worker *worker;

	worker = kzalloc_node(sizeof(*worker), GFP_KERNEL, node);
	if (worker) {
		INIT_LIST_HEAD(&worker->entry);
		INIT_LIST_HEAD(&worker->scheduled);
		INIT_LIST_HEAD(&worker->node);
		/* on creation a worker is in !idle && prep state */
		worker->flags = WORKER_PREP;
	}
	return worker;
}

static cpumask_t *pool_allowed_cpus(struct worker_pool *pool)
{
	if (pool->cpu < 0 && pool->attrs->affn_strict)
		return pool->attrs->__pod_cpumask;
	else
		return pool->attrs->cpumask;
}

/**
 * worker_attach_to_pool() - attach a worker to a pool
 * @worker: worker to be attached
 * @pool: the target pool
 *
 * Attach @worker to @pool.  Once attached, the %WORKER_UNBOUND flag and
 * cpu-binding of @worker are kept coordinated with the pool across
 * cpu-[un]hotplugs.
 */
static void worker_attach_to_pool(struct worker *worker,
				  struct worker_pool *pool)
{
	mutex_lock(&wq_pool_attach_mutex);

	/*
	 * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains stable
	 * across this function. See the comments above the flag definition for
	 * details. BH workers are, while per-CPU, always DISASSOCIATED.
	 */
	if (pool->flags & POOL_DISASSOCIATED) {
		worker->flags |= WORKER_UNBOUND;
	} else {
		WARN_ON_ONCE(pool->flags & POOL_BH);
		kthread_set_per_cpu(worker->task, pool->cpu);
	}

	if (worker->rescue_wq)
		set_cpus_allowed_ptr(worker->task, pool_allowed_cpus(pool));

	list_add_tail(&worker->node, &pool->workers);
	worker->pool = pool;

	mutex_unlock(&wq_pool_attach_mutex);
}

static void unbind_worker(struct worker *worker)
{
	lockdep_assert_held(&wq_pool_attach_mutex);

	kthread_set_per_cpu(worker->task, -1);
	if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask))
		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0);
	else
		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
}


static void detach_worker(struct worker *worker)
{
	lockdep_assert_held(&wq_pool_attach_mutex);

	unbind_worker(worker);
	list_del(&worker->node);
}

/**
 * worker_detach_from_pool() - detach a worker from its pool
 * @worker: worker which is attached to its pool
 *
 * Undo the attaching which had been done in worker_attach_to_pool().  The
 * caller worker shouldn't access to the pool after detached except it has
 * other reference to the pool.
 */
static void worker_detach_from_pool(struct worker *worker)
{
	struct worker_pool *pool = worker->pool;

	/* there is one permanent BH worker per CPU which should never detach */
	WARN_ON_ONCE(pool->flags & POOL_BH);

	mutex_lock(&wq_pool_attach_mutex);
	detach_worker(worker);
	worker->pool = NULL;
	mutex_unlock(&wq_pool_attach_mutex);

	/* clear leftover flags without pool->lock after it is detached */
	worker->flags &= ~(WORKER_UNBOUND | WORKER_REBOUND);
}

static int format_worker_id(char *buf, size_t size, struct worker *worker,
			    struct worker_pool *pool)
{
	if (worker->rescue_wq)
		return scnprintf(buf, size, "kworker/R-%s",
				 worker->rescue_wq->name);

	if (pool) {
		if (pool->cpu >= 0)
			return scnprintf(buf, size, "kworker/%d:%d%s",
					 pool->cpu, worker->id,
					 pool->attrs->nice < 0  ? "H" : "");
		else
			return scnprintf(buf, size, "kworker/u%d:%d",
					 pool->id, worker->id);
	} else {
		return scnprintf(buf, size, "kworker/dying");
	}
}

/**
 * create_worker - create a new workqueue worker
 * @pool: pool the new worker will belong to
 *
 * Create and start a new worker which is attached to @pool.
 *
 * CONTEXT:
 * Might sleep.  Does GFP_KERNEL allocations.
 *
 * Return:
 * Pointer to the newly created worker.
 */
static struct worker *create_worker(struct worker_pool *pool)
{
	struct worker *worker;
	int id;

	/* ID is needed to determine kthread name */
	id = ida_alloc(&pool->worker_ida, GFP_KERNEL);
	if (id < 0) {
		pr_err_once("workqueue: Failed to allocate a worker ID: %pe\n",
			    ERR_PTR(id));
		return NULL;
	}

	worker = alloc_worker(pool->node);
	if (!worker) {
		pr_err_once("workqueue: Failed to allocate a worker\n");
		goto fail;
	}

	worker->id = id;

	if (!(pool->flags & POOL_BH)) {
		char id_buf[WORKER_ID_LEN];

		format_worker_id(id_buf, sizeof(id_buf), worker, pool);
		worker->task = kthread_create_on_node(worker_thread, worker,
						      pool->node, "%s", id_buf);
		if (IS_ERR(worker->task)) {
			if (PTR_ERR(worker->task) == -EINTR) {
				pr_err("workqueue: Interrupted when creating a worker thread \"%s\"\n",
				       id_buf);
			} else {
				pr_err_once("workqueue: Failed to create a worker thread: %pe",
					    worker->task);
			}
			goto fail;
		}

		set_user_nice(worker->task, pool->attrs->nice);
		kthread_bind_mask(worker->task, pool_allowed_cpus(pool));
	}

	/* successful, attach the worker to the pool */
	worker_attach_to_pool(worker, pool);

	/* start the newly created worker */
	raw_spin_lock_irq(&pool->lock);

	worker->pool->nr_workers++;
	worker_enter_idle(worker);

	/*
	 * @worker is waiting on a completion in kthread() and will trigger hung
	 * check if not woken up soon. As kick_pool() is noop if @pool is empty,
	 * wake it up explicitly.
	 */
	if (worker->task)
		wake_up_process(worker->task);

	raw_spin_unlock_irq(&pool->lock);

	return worker;

fail:
	ida_free(&pool->worker_ida, id);
	kfree(worker);
	return NULL;
}

static void detach_dying_workers(struct list_head *cull_list)
{
	struct worker *worker;

	list_for_each_entry(worker, cull_list, entry)
		detach_worker(worker);
}

static void reap_dying_workers(struct list_head *cull_list)
{
	struct worker *worker, *tmp;

	list_for_each_entry_safe(worker, tmp, cull_list, entry) {
		list_del_init(&worker->entry);
		kthread_stop_put(worker->task);
		kfree(worker);
	}
}

/**
 * set_worker_dying - Tag a worker for destruction
 * @worker: worker to be destroyed
 * @list: transfer worker away from its pool->idle_list and into list
 *
 * Tag @worker for destruction and adjust @pool stats accordingly.  The worker
 * should be idle.
 *
 * CONTEXT:
 * raw_spin_lock_irq(pool->lock).
 */
static void set_worker_dying(struct worker *worker, struct list_head *list)
{
	struct worker_pool *pool = worker->pool;

	lockdep_assert_held(&pool->lock);
	lockdep_assert_held(&wq_pool_attach_mutex);

	/* sanity check frenzy */
	if (WARN_ON(worker->current_work) ||
	    WARN_ON(!list_empty(&worker->scheduled)) ||
	    WARN_ON(!(worker->flags & WORKER_IDLE)))
		return;

	pool->nr_workers--;
	pool->nr_idle--;

	worker->flags |= WORKER_DIE;

	list_move(&worker->entry, list);

	/* get an extra task struct reference for later kthread_stop_put() */
	get_task_struct(worker->task);
}

/**
 * idle_worker_timeout - check if some idle workers can now be deleted.
 * @t: The pool's idle_timer that just expired
 *
 * The timer is armed in worker_enter_idle(). Note that it isn't disarmed in
 * worker_leave_idle(), as a worker flicking between idle and active while its
 * pool is at the too_many_workers() tipping point would cause too much timer
 * housekeeping overhead. Since IDLE_WORKER_TIMEOUT is long enough, we just let
 * it expire and re-evaluate things from there.
 */
static void idle_worker_timeout(struct timer_list *t)
{
	struct worker_pool *pool = timer_container_of(pool, t, idle_timer);
	bool do_cull = false;

	if (work_pending(&pool->idle_cull_work))
		return;

	raw_spin_lock_irq(&pool->lock);

	if (too_many_workers(pool)) {
		struct worker *worker;
		unsigned long expires;

		/* idle_list is kept in LIFO order, check the last one */
		worker = list_last_entry(&pool->idle_list, struct worker, entry);
		expires = worker->last_active + IDLE_WORKER_TIMEOUT;
		do_cull = !time_before(jiffies, expires);

		if (!do_cull)
			mod_timer(&pool->idle_timer, expires);
	}
	raw_spin_unlock_irq(&pool->lock);

	if (do_cull)
		queue_work(system_dfl_wq, &pool->idle_cull_work);
}

/**
 * idle_cull_fn - cull workers that have been idle for too long.
 * @work: the pool's work for handling these idle workers
 *
 * This goes through a pool's idle workers and gets rid of those that have been
 * idle for at least IDLE_WORKER_TIMEOUT seconds.
 *
 * We don't want to disturb isolated CPUs because of a pcpu kworker being
 * culled, so this also resets worker affinity. This requires a sleepable
 * context, hence the split between timer callback and work item.
 */
static void idle_cull_fn(struct work_struct *work)
{
	struct worker_pool *pool = container_of(work, struct worker_pool, idle_cull_work);
	LIST_HEAD(cull_list);

	/*
	 * Grabbing wq_pool_attach_mutex here ensures an already-running worker
	 * cannot proceed beyong set_pf_worker() in its self-destruct path.
	 * This is required as a previously-preempted worker could run after
	 * set_worker_dying() has happened but before detach_dying_workers() did.
	 */
	mutex_lock(&wq_pool_attach_mutex);
	raw_spin_lock_irq(&pool->lock);

	while (too_many_workers(pool)) {
		struct worker *worker;
		unsigned long expires;

		worker = list_last_entry(&pool->idle_list, struct worker, entry);
		expires = worker->last_active + IDLE_WORKER_TIMEOUT;

		if (time_before(jiffies, expires)) {
			mod_timer(&pool->idle_timer, expires);
			break;
		}

		set_worker_dying(worker, &cull_list);
	}

	raw_spin_unlock_irq(&pool->lock);
	detach_dying_workers(&cull_list);
	mutex_unlock(&wq_pool_attach_mutex);

	reap_dying_workers(&cull_list);
}

static void send_mayday(struct pool_workqueue *pwq)
{
	struct workqueue_struct *wq = pwq->wq;

	lockdep_assert_held(&wq_mayday_lock);

	if (!wq->rescuer)
		return;

	/* mayday mayday mayday */
	if (list_empty(&pwq->mayday_node)) {
		/*
		 * If @pwq is for an unbound wq, its base ref may be put at
		 * any time due to an attribute change.  Pin @pwq until the
		 * rescuer is done with it.
		 */
		get_pwq(pwq);
		list_add_tail(&pwq->mayday_node, &wq->maydays);
		wake_up_process(wq->rescuer->task);
		pwq->stats[PWQ_STAT_MAYDAY]++;
	}
}

static void pool_mayday_timeout(struct timer_list *t)
{
	struct worker_pool *pool = timer_container_of(pool, t, mayday_timer);
	struct work_struct *work;

	raw_spin_lock_irq(&pool->lock);
	raw_spin_lock(&wq_mayday_lock);		/* for wq->maydays */

	if (need_to_create_worker(pool)) {
		/*
		 * We've been trying to create a new worker but
		 * haven't been successful.  We might be hitting an
		 * allocation deadlock.  Send distress signals to
		 * rescuers.
		 */
		list_for_each_entry(work, &pool->worklist, entry)
			send_mayday(get_work_pwq(work));
	}

	raw_spin_unlock(&wq_mayday_lock);
	raw_spin_unlock_irq(&pool->lock);

	mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
}

/**
 * maybe_create_worker - create a new worker if necessary
 * @pool: pool to create a new worker for
 *
 * Create a new worker for @pool if necessary.  @pool is guaranteed to
 * have at least one idle worker on return from this function.  If
 * creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
 * sent to all rescuers with works scheduled on @pool to resolve
 * possible allocation deadlock.
 *
 * On return, need_to_create_worker() is guaranteed to be %false and
 * may_start_working() %true.
 *
 * LOCKING:
 * raw_spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.  Does GFP_KERNEL allocations.  Called only from
 * manager.
 */
static void maybe_create_worker(struct worker_pool *pool)
__releases(&pool->lock)
__acquires(&pool->lock)
{
restart:
	raw_spin_unlock_irq(&pool->lock);

	/* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
	mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);

	while (true) {
		if (create_worker(pool) || !need_to_create_worker(pool))
			break;

		schedule_timeout_interruptible(CREATE_COOLDOWN);

		if (!need_to_create_worker(pool))
			break;
	}

	timer_delete_sync(&pool->mayday_timer);
	raw_spin_lock_irq(&pool->lock);
	/*
	 * This is necessary even after a new worker was just successfully
	 * created as @pool->lock was dropped and the new worker might have
	 * already become busy.
	 */
	if (need_to_create_worker(pool))
		goto restart;
}

#ifdef CONFIG_PREEMPT_RT
static void worker_lock_callback(struct worker_pool *pool)
{
	spin_lock(&pool->cb_lock);
}

static void worker_unlock_callback(struct worker_pool *pool)
{
	spin_unlock(&pool->cb_lock);
}

static void workqueue_callback_cancel_wait_running(struct worker_pool *pool)
{
	spin_lock(&pool->cb_lock);
	spin_unlock(&pool->cb_lock);
}

#else

static void worker_lock_callback(struct worker_pool *pool) { }
static void worker_unlock_callback(struct worker_pool *pool) { }
static void workqueue_callback_cancel_wait_running(struct worker_pool *pool) { }

#endif

/**
 * manage_workers - manage worker pool
 * @worker: self
 *
 * Assume the manager role and manage the worker pool @worker belongs
 * to.  At any given time, there can be only zero or one manager per
 * pool.  The exclusion is handled automatically by this function.
 *
 * The caller can safely start processing works on false return.  On
 * true return, it's guaranteed that need_to_create_worker() is false
 * and may_start_working() is true.
 *
 * CONTEXT:
 * raw_spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.  Does GFP_KERNEL allocations.
 *
 * Return:
 * %false if the pool doesn't need management and the caller can safely
 * start processing works, %true if management function was performed and
 * the conditions that the caller verified before calling the function may
 * no longer be true.
 */
static bool manage_workers(struct worker *worker)
{
	struct worker_pool *pool = worker->pool;

	if (pool->flags & POOL_MANAGER_ACTIVE)
		return false;

	pool->flags |= POOL_MANAGER_ACTIVE;
	pool->manager = worker;

	maybe_create_worker(pool);

	pool->manager = NULL;
	pool->flags &= ~POOL_MANAGER_ACTIVE;
	rcuwait_wake_up(&manager_wait);
	return true;
}

/**
 * process_one_work - process single work
 * @worker: self
 * @work: work to process
 *
 * Process @work.  This function contains all the logics necessary to
 * process a single work including synchronization against and
 * interaction with other workers on the same cpu, queueing and
 * flushing.  As long as context requirement is met, any worker can
 * call this function to process a work.
 *
 * CONTEXT:
 * raw_spin_lock_irq(pool->lock) which is released and regrabbed.
 */
static void process_one_work(struct worker *worker, struct work_struct *work)
__releases(&pool->lock)
__acquires(&pool->lock)
{
	struct pool_workqueue *pwq = get_work_pwq(work);
	struct worker_pool *pool = worker->pool;
	unsigned long work_data;
	int lockdep_start_depth, rcu_start_depth;
	bool bh_draining = pool->flags & POOL_BH_DRAINING;
#ifdef CONFIG_LOCKDEP
	/*
	 * It is permissible to free the struct work_struct from
	 * inside the function that is called from it, this we need to
	 * take into account for lockdep too.  To avoid bogus "held
	 * lock freed" warnings as well as problems when looking into
	 * work->lockdep_map, make a copy and use that here.
	 */
	struct lockdep_map lockdep_map;

	lockdep_copy_map(&lockdep_map, &work->lockdep_map);
#endif
	/* ensure we're on the correct CPU */
	WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
		     raw_smp_processor_id() != pool->cpu);

	/* claim and dequeue */
	debug_work_deactivate(work);
	hash_add(pool->busy_hash, &worker->hentry, (unsigned long)work);
	worker->current_work = work;
	worker->current_func = work->func;
	worker->current_pwq = pwq;
	if (worker->task)
		worker->current_at = worker->task->se.sum_exec_runtime;
	worker->current_start = jiffies;
	work_data = *work_data_bits(work);
	worker->current_color = get_work_color(work_data);

	/*
	 * Record wq name for cmdline and debug reporting, may get
	 * overridden through set_worker_desc().
	 */
	strscpy(worker->desc, pwq->wq->name, WORKER_DESC_LEN);

	list_del_init(&work->entry);

	/*
	 * CPU intensive works don't participate in concurrency management.
	 * They're the scheduler's responsibility.  This takes @worker out
	 * of concurrency management and the next code block will chain
	 * execution of the pending work items.
	 */
	if (unlikely(pwq->wq->flags & WQ_CPU_INTENSIVE))
		worker_set_flags(worker, WORKER_CPU_INTENSIVE);

	/*
	 * Kick @pool if necessary. It's always noop for per-cpu worker pools
	 * since nr_running would always be >= 1 at this point. This is used to
	 * chain execution of the pending work items for WORKER_NOT_RUNNING
	 * workers such as the UNBOUND and CPU_INTENSIVE ones.
	 */
	kick_pool(pool);

	/*
	 * Record the last pool and clear PENDING which should be the last
	 * update to @work.  Also, do this inside @pool->lock so that
	 * PENDING and queued state changes happen together while IRQ is
	 * disabled.
	 */
	set_work_pool_and_clear_pending(work, pool->id, pool_offq_flags(pool));

	pwq->stats[PWQ_STAT_STARTED]++;
	raw_spin_unlock_irq(&pool->lock);

	rcu_start_depth = rcu_preempt_depth();
	lockdep_start_depth = lockdep_depth(current);
	/* see drain_dead_softirq_workfn() */
	if (!bh_draining)
		lock_map_acquire(pwq->wq->lockdep_map);
	lock_map_acquire(&lockdep_map);
	/*
	 * Strictly speaking we should mark the invariant state without holding
	 * any locks, that is, before these two lock_map_acquire()'s.
	 *
	 * However, that would result in:
	 *
	 *   A(W1)
	 *   WFC(C)
	 *		A(W1)
	 *		C(C)
	 *
	 * Which would create W1->C->W1 dependencies, even though there is no
	 * actual deadlock possible. There are two solutions, using a
	 * read-recursive acquire on the work(queue) 'locks', but this will then
	 * hit the lockdep limitation on recursive locks, or simply discard
	 * these locks.
	 *
	 * AFAICT there is no possible deadlock scenario between the
	 * flush_work() and complete() primitives (except for single-threaded
	 * workqueues), so hiding them isn't a problem.
	 */
	lockdep_invariant_state(true);
	trace_workqueue_execute_start(work);
	worker->current_func(work);
	/*
	 * While we must be careful to not use "work" after this, the trace
	 * point will only record its address.
	 */
	trace_workqueue_execute_end(work, worker->current_func);

	lock_map_release(&lockdep_map);
	if (!bh_draining)
		lock_map_release(pwq->wq->lockdep_map);

	if (unlikely((worker->task && in_atomic()) ||
		     lockdep_depth(current) != lockdep_start_depth ||
		     rcu_preempt_depth() != rcu_start_depth)) {
		pr_err("BUG: workqueue leaked atomic, lock or RCU: %s[%d]\n"
		       "     preempt=0x%08x lock=%d->%d RCU=%d->%d workfn=%ps\n",
		       current->comm, task_pid_nr(current), preempt_count(),
		       lockdep_start_depth, lockdep_depth(current),
		       rcu_start_depth, rcu_preempt_depth(),
		       worker->current_func);
		debug_show_held_locks(current);
		dump_stack();
	}

	/*
	 * The following prevents a kworker from hogging CPU on !PREEMPTION
	 * kernels, where a requeueing work item waiting for something to
	 * happen could deadlock with stop_machine as such work item could
	 * indefinitely requeue itself while all other CPUs are trapped in
	 * stop_machine. At the same time, report a quiescent RCU state so
	 * the same condition doesn't freeze RCU.
	 */
	if (worker->task)
		cond_resched();

	raw_spin_lock_irq(&pool->lock);

	pwq->stats[PWQ_STAT_COMPLETED]++;

	/*
	 * In addition to %WQ_CPU_INTENSIVE, @worker may also have been marked
	 * CPU intensive by wq_worker_tick() if @work hogged CPU longer than
	 * wq_cpu_intensive_thresh_us. Clear it.
	 */
	worker_clr_flags(worker, WORKER_CPU_INTENSIVE);

	/* tag the worker for identification in schedule() */
	worker->last_func = worker->current_func;

	/* we're done with it, release */
	hash_del(&worker->hentry);
	worker->current_work = NULL;
	worker->current_func = NULL;
	worker->current_pwq = NULL;
	worker->current_color = INT_MAX;

	/* must be the last step, see the function comment */
	pwq_dec_nr_in_flight(pwq, work_data);
}

/**
 * process_scheduled_works - process scheduled works
 * @worker: self
 *
 * Process all scheduled works.  Please note that the scheduled list
 * may change while processing a work, so this function repeatedly
 * fetches a work from the top and executes it.
 *
 * CONTEXT:
 * raw_spin_lock_irq(pool->lock) which may be released and regrabbed
 * multiple times.
 */
static void process_scheduled_works(struct worker *worker)
{
	struct work_struct *work;
	bool first = true;

	while ((work = list_first_entry_or_null(&worker->scheduled,
						struct work_struct, entry))) {
		if (first) {
			worker->pool->last_progress_ts = jiffies;
			first = false;
		}
		process_one_work(worker, work);
	}
}

static void set_pf_worker(bool val)
{
	mutex_lock(&wq_pool_attach_mutex);
	if (val)
		current->flags |= PF_WQ_WORKER;
	else
		current->flags &= ~PF_WQ_WORKER;
	mutex_unlock(&wq_pool_attach_mutex);
}

/**
 * worker_thread - the worker thread function
 * @__worker: self
 *
 * The worker thread function.  All workers belong to a worker_pool -
 * either a per-cpu one or dynamic unbound one.  These workers process all
 * work items regardless of their specific target workqueue.  The only
 * exception is work items which belong to workqueues with a rescuer which
 * will be explained in rescuer_thread().
 *
 * Return: 0
 */
static int worker_thread(void *__worker)
{
	struct worker *worker = __worker;
	struct worker_pool *pool = worker->pool;

	/* tell the scheduler that this is a workqueue worker */
	set_pf_worker(true);
woke_up:
	raw_spin_lock_irq(&pool->lock);

	/* am I supposed to die? */
	if (unlikely(worker->flags & WORKER_DIE)) {
		raw_spin_unlock_irq(&pool->lock);
		set_pf_worker(false);
		/*
		 * The worker is dead and PF_WQ_WORKER is cleared, worker->pool
		 * shouldn't be accessed, reset it to NULL in case otherwise.
		 */
		worker->pool = NULL;
		ida_free(&pool->worker_ida, worker->id);
		return 0;
	}

	worker_leave_idle(worker);
recheck:
	/* no more worker necessary? */
	if (!need_more_worker(pool))
		goto sleep;

	/* do we need to manage? */
	if (unlikely(!may_start_working(pool)) && manage_workers(worker))
		goto recheck;

	/*
	 * ->scheduled list can only be filled while a worker is
	 * preparing to process a work or actually processing it.
	 * Make sure nobody diddled with it while I was sleeping.
	 */
	WARN_ON_ONCE(!list_empty(&worker->scheduled));

	/*
	 * Finish PREP stage.  We're guaranteed to have at least one idle
	 * worker or that someone else has already assumed the manager
	 * role.  This is where @worker starts participating in concurrency
	 * management if applicable and concurrency management is restored
	 * after being rebound.  See rebind_workers() for details.
	 */
	worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);

	do {
		struct work_struct *work =
			list_first_entry(&pool->worklist,
					 struct work_struct, entry);

		if (assign_work(work, worker, NULL))
			process_scheduled_works(worker);
	} while (keep_working(pool));

	worker_set_flags(worker, WORKER_PREP);
sleep:
	/*
	 * pool->lock is held and there's no work to process and no need to
	 * manage, sleep.  Workers are woken up only while holding
	 * pool->lock or from local cpu, so setting the current state
	 * before releasing pool->lock is enough to prevent losing any
	 * event.
	 */
	worker_enter_idle(worker);
	__set_current_state(TASK_IDLE);
	raw_spin_unlock_irq(&pool->lock);
	schedule();
	goto woke_up;
}

static bool assign_rescuer_work(struct pool_workqueue *pwq, struct worker *rescuer)
{
	struct worker_pool *pool = pwq->pool;
	struct work_struct *cursor = &pwq->mayday_cursor;
	struct work_struct *work, *n;

	/* have work items to rescue? */
	if (!pwq->nr_active)
		return false;

	/* need rescue? */
	if (!need_to_create_worker(pool)) {
		/*
		 * The pool has idle workers and doesn't need the rescuer, so it
		 * could simply return false here.
		 *
		 * However, the memory pressure might not be fully relieved.
		 * In PERCPU pool with concurrency enabled, having idle workers
		 * does not necessarily mean memory pressure is gone; it may
		 * simply mean regular workers have woken up, completed their
		 * work, and gone idle again due to concurrency limits.
		 *
		 * In this case, those working workers may later sleep again,
		 * the pool may run out of idle workers, and it will have to
		 * allocate new ones and wait for the timer to send mayday,
		 * causing unnecessary delay - especially if memory pressure
		 * was never resolved throughout.
		 *
		 * Do more work if memory pressure is still on to reduce
		 * relapse, using (pool->flags & POOL_MANAGER_ACTIVE), though
		 * not precisely, unless there are other PWQs needing help.
		 */
		if (!(pool->flags & POOL_MANAGER_ACTIVE) ||
		    !list_empty(&pwq->wq->maydays))
			return false;
	}

	/* search from the start or cursor if available */
	if (list_empty(&cursor->entry))
		work = list_first_entry(&pool->worklist, struct work_struct, entry);
	else
		work = list_next_entry(cursor, entry);

	/* find the next work item to rescue */
	list_for_each_entry_safe_from(work, n, &pool->worklist, entry) {
		if (get_work_pwq(work) == pwq && assign_work(work, rescuer, &n)) {
			pwq->stats[PWQ_STAT_RESCUED]++;
			/* put the cursor for next search */
			list_move_tail(&cursor->entry, &n->entry);
			return true;
		}
	}

	return false;
}

/**
 * rescuer_thread - the rescuer thread function
 * @__rescuer: self
 *
 * Workqueue rescuer thread function.  There's one rescuer for each
 * workqueue which has WQ_MEM_RECLAIM set.
 *
 * Regular work processing on a pool may block trying to create a new
 * worker which uses GFP_KERNEL allocation which has slight chance of
 * developing into deadlock if some works currently on the same queue
 * need to be processed to satisfy the GFP_KERNEL allocation.  This is
 * the problem rescuer solves.
 *
 * When such condition is possible, the pool summons rescuers of all
 * workqueues which have works queued on the pool and let them process
 * those works so that forward progress can be guaranteed.
 *
 * This should happen rarely.
 *
 * Return: 0
 */
static int rescuer_thread(void *__rescuer)
{
	struct worker *rescuer = __rescuer;
	struct workqueue_struct *wq = rescuer->rescue_wq;
	bool should_stop;

	set_user_nice(current, RESCUER_NICE_LEVEL);

	/*
	 * Mark rescuer as worker too.  As WORKER_PREP is never cleared, it
	 * doesn't participate in concurrency management.
	 */
	set_pf_worker(true);
repeat:
	set_current_state(TASK_IDLE);

	/*
	 * By the time the rescuer is requested to stop, the workqueue
	 * shouldn't have any work pending, but @wq->maydays may still have
	 * pwq(s) queued.  This can happen by non-rescuer workers consuming
	 * all the work items before the rescuer got to them.  Go through
	 * @wq->maydays processing before acting on should_stop so that the
	 * list is always empty on exit.
	 */
	should_stop = kthread_should_stop();

	/* see whether any pwq is asking for help */
	raw_spin_lock_irq(&wq_mayday_lock);

	while (!list_empty(&wq->maydays)) {
		struct pool_workqueue *pwq = list_first_entry(&wq->maydays,
					struct pool_workqueue, mayday_node);
		struct worker_pool *pool = pwq->pool;
		unsigned int count = 0;

		__set_current_state(TASK_RUNNING);
		list_del_init(&pwq->mayday_node);

		raw_spin_unlock_irq(&wq_mayday_lock);

		worker_attach_to_pool(rescuer, pool);

		raw_spin_lock_irq(&pool->lock);

		WARN_ON_ONCE(!list_empty(&rescuer->scheduled));

		while (assign_rescuer_work(pwq, rescuer)) {
			process_scheduled_works(rescuer);

			/*
			 * If the per-turn work item limit is reached and other
			 * PWQs are in mayday, requeue mayday for this PWQ and
			 * let the rescuer handle the other PWQs first.
			 */
			if (++count > RESCUER_BATCH && !list_empty(&pwq->wq->maydays) &&
			    pwq->nr_active && need_to_create_worker(pool)) {
				raw_spin_lock(&wq_mayday_lock);
				send_mayday(pwq);
				raw_spin_unlock(&wq_mayday_lock);
				break;
			}
		}

		/* The cursor can not be left behind without the rescuer watching it. */
		if (!list_empty(&pwq->mayday_cursor.entry) && list_empty(&pwq->mayday_node))
			list_del_init(&pwq->mayday_cursor.entry);

		/*
		 * Leave this pool. Notify regular workers; otherwise, we end up
		 * with 0 concurrency and stalling the execution.
		 */
		kick_pool(pool);

		raw_spin_unlock_irq(&pool->lock);

		worker_detach_from_pool(rescuer);

		/*
		 * Put the reference grabbed by send_mayday().  @pool might
		 * go away any time after it.
		 */
		put_pwq_unlocked(pwq);

		raw_spin_lock_irq(&wq_mayday_lock);
	}

	raw_spin_unlock_irq(&wq_mayday_lock);

	if (should_stop) {
		__set_current_state(TASK_RUNNING);
		set_pf_worker(false);
		return 0;
	}

	/* rescuers should never participate in concurrency management */
	WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
	schedule();
	goto repeat;
}

static void bh_worker(struct worker *worker)
{
	struct worker_pool *pool = worker->pool;
	int nr_restarts = BH_WORKER_RESTARTS;
	unsigned long end = jiffies + BH_WORKER_JIFFIES;

	worker_lock_callback(pool);
	raw_spin_lock_irq(&pool->lock);
	worker_leave_idle(worker);

	/*
	 * This function follows the structure of worker_thread(). See there for
	 * explanations on each step.
	 */
	if (!need_more_worker(pool))
		goto done;

	WARN_ON_ONCE(!list_empty(&worker->scheduled));
	worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND);

	do {
		struct work_struct *work =
			list_first_entry(&pool->worklist,
					 struct work_struct, entry);

		if (assign_work(work, worker, NULL))
			process_scheduled_works(worker);
	} while (keep_working(pool) &&
		 --nr_restarts && time_before(jiffies, end));

	worker_set_flags(worker, WORKER_PREP);
done:
	worker_enter_idle(worker);
	kick_pool(pool);
	raw_spin_unlock_irq(&pool->lock);
	worker_unlock_callback(pool);
}

/*
 * TODO: Convert all tasklet users to workqueue and use softirq directly.
 *
 * This is currently called from tasklet[_hi]action() and thus is also called
 * whenever there are tasklets to run. Let's do an early exit if there's nothing
 * queued. Once conversion from tasklet is complete, the need_more_worker() test
 * can be dropped.
 *
 * After full conversion, we'll add worker->softirq_action, directly use the
 * softirq action and obtain the worker pointer from the softirq_action pointer.
 */
void workqueue_softirq_action(bool highpri)
{
	struct worker_pool *pool =
		&per_cpu(bh_worker_pools, smp_processor_id())[highpri];
	if (need_more_worker(pool))
		bh_worker(list_first_entry(&pool->workers, struct worker, node));
}

struct wq_drain_dead_softirq_work {
	struct work_struct	work;
	struct worker_pool	*pool;
	struct completion	done;
};

static void drain_dead_softirq_workfn(struct work_struct *work)
{
	struct wq_drain_dead_softirq_work *dead_work =
		container_of(work, struct wq_drain_dead_softirq_work, work);
	struct worker_pool *pool = dead_work->pool;
	bool repeat;

	/*
	 * @pool's CPU is dead and we want to execute its still pending work
	 * items from this BH work item which is running on a different CPU. As
	 * its CPU is dead, @pool can't be kicked and, as work execution path
	 * will be nested, a lockdep annotation needs to be suppressed. Mark
	 * @pool with %POOL_BH_DRAINING for the special treatments.
	 */
	raw_spin_lock_irq(&pool->lock);
	pool->flags |= POOL_BH_DRAINING;
	raw_spin_unlock_irq(&pool->lock);

	bh_worker(list_first_entry(&pool->workers, struct worker, node));

	raw_spin_lock_irq(&pool->lock);
	pool->flags &= ~POOL_BH_DRAINING;
	repeat = need_more_worker(pool);
	raw_spin_unlock_irq(&pool->lock);

	/*
	 * bh_worker() might hit consecutive execution limit and bail. If there
	 * still are pending work items, reschedule self and return so that we
	 * don't hog this CPU's BH.
	 */
	if (repeat) {
		if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
			queue_work(system_bh_highpri_wq, work);
		else
			queue_work(system_bh_wq, work);
	} else {
		complete(&dead_work->done);
	}
}

/*
 * @cpu is dead. Drain the remaining BH work items on the current CPU. It's
 * possible to allocate dead_work per CPU and avoid flushing. However, then we
 * have to worry about draining overlapping with CPU coming back online or
 * nesting (one CPU's dead_work queued on another CPU which is also dead and so
 * on). Let's keep it simple and drain them synchronously. These are BH work
 * items which shouldn't be requeued on the same pool. Shouldn't take long.
 */
void workqueue_softirq_dead(unsigned int cpu)
{
	int i;

	for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
		struct worker_pool *pool = &per_cpu(bh_worker_pools, cpu)[i];
		struct wq_drain_dead_softirq_work dead_work;

		if (!need_more_worker(pool))
			continue;

		INIT_WORK_ONSTACK(&dead_work.work, drain_dead_softirq_workfn);
		dead_work.pool = pool;
		init_completion(&dead_work.done);

		if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
			queue_work(system_bh_highpri_wq, &dead_work.work);
		else
			queue_work(system_bh_wq, &dead_work.work);

		wait_for_completion(&dead_work.done);
		destroy_work_on_stack(&dead_work.work);
	}
}

/**
 * check_flush_dependency - check for flush dependency sanity
 * @target_wq: workqueue being flushed
 * @target_work: work item being flushed (NULL for workqueue flushes)
 * @from_cancel: are we called from the work cancel path
 *
 * %current is trying to flush the whole @target_wq or @target_work on it.
 * If this is not the cancel path (which implies work being flushed is either
 * already running, or will not be at all), check if @target_wq doesn't have
 * %WQ_MEM_RECLAIM and verify that %current is not reclaiming memory or running
 * on a workqueue which doesn't have %WQ_MEM_RECLAIM as that can break forward-
 * progress guarantee leading to a deadlock.
 */
static void check_flush_dependency(struct workqueue_struct *target_wq,
				   struct work_struct *target_work,
				   bool from_cancel)
{
	work_func_t target_func;
	struct worker *worker;

	if (from_cancel || target_wq->flags & WQ_MEM_RECLAIM)
		return;

	worker = current_wq_worker();
	target_func = target_work ? target_work->func : NULL;

	WARN_ONCE(current->flags & PF_MEMALLOC,
		  "workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%ps",
		  current->pid, current->comm, target_wq->name, target_func);
	WARN_ONCE(worker && ((worker->current_pwq->wq->flags &
			      (WQ_MEM_RECLAIM | __WQ_LEGACY)) == WQ_MEM_RECLAIM),
		  "workqueue: WQ_MEM_RECLAIM %s:%ps is flushing !WQ_MEM_RECLAIM %s:%ps",
		  worker->current_pwq->wq->name, worker->current_func,
		  target_wq->name, target_func);
}

struct wq_barrier {
	struct work_struct	work;
	struct completion	done;
	struct task_struct	*task;	/* purely informational */
};

static void wq_barrier_func(struct work_struct *work)
{
	struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
	complete(&barr->done);
}

/**
 * insert_wq_barrier - insert a barrier work
 * @pwq: pwq to insert barrier into
 * @barr: wq_barrier to insert
 * @target: target work to attach @barr to
 * @worker: worker currently executing @target, NULL if @target is not executing
 *
 * @barr is linked to @target such that @barr is completed only after
 * @target finishes execution.  Please note that the ordering
 * guarantee is observed only with respect to @target and on the local
 * cpu.
 *
 * Currently, a queued barrier can't be canceled.  This is because
 * try_to_grab_pending() can't determine whether the work to be
 * grabbed is at the head of the queue and thus can't clear LINKED
 * flag of the previous work while there must be a valid next work
 * after a work with LINKED flag set.
 *
 * Note that when @worker is non-NULL, @target may be modified
 * underneath us, so we can't reliably determine pwq from @target.
 *
 * CONTEXT:
 * raw_spin_lock_irq(pool->lock).
 */
static void insert_wq_barrier(struct pool_workqueue *pwq,
			      struct wq_barrier *barr,
			      struct work_struct *target, struct worker *worker)
{
	static __maybe_unused struct lock_class_key bh_key, thr_key;
	unsigned int work_flags = 0;
	unsigned int work_color;
	struct list_head *head;

	/*
	 * debugobject calls are safe here even with pool->lock locked
	 * as we know for sure that this will not trigger any of the
	 * checks and call back into the fixup functions where we
	 * might deadlock.
	 *
	 * BH and threaded workqueues need separate lockdep keys to avoid
	 * spuriously triggering "inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W}
	 * usage".
	 */
	INIT_WORK_ONSTACK_KEY(&barr->work, wq_barrier_func,
			      (pwq->wq->flags & WQ_BH) ? &bh_key : &thr_key);
	__set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));

	init_completion_map(&barr->done, &target->lockdep_map);

	barr->task = current;

	/* The barrier work item does not participate in nr_active. */
	work_flags |= WORK_STRUCT_INACTIVE;

	/*
	 * If @target is currently being executed, schedule the
	 * barrier to the worker; otherwise, put it after @target.
	 */
	if (worker) {
		head = worker->scheduled.next;
		work_color = worker->current_color;
	} else {
		unsigned long *bits = work_data_bits(target);

		head = target->entry.next;
		/* there can already be other linked works, inherit and set */
		work_flags |= *bits & WORK_STRUCT_LINKED;
		work_color = get_work_color(*bits);
		__set_bit(WORK_STRUCT_LINKED_BIT, bits);
	}

	pwq->nr_in_flight[work_color]++;
	work_flags |= work_color_to_flags(work_color);

	insert_work(pwq, &barr->work, head, work_flags);
}

/**
 * flush_workqueue_prep_pwqs - prepare pwqs for workqueue flushing
 * @wq: workqueue being flushed
 * @flush_color: new flush color, < 0 for no-op
 * @work_color: new work color, < 0 for no-op
 *
 * Prepare pwqs for workqueue flushing.
 *
 * If @flush_color is non-negative, flush_color on all pwqs should be
 * -1.  If no pwq has in-flight commands at the specified color, all
 * pwq->flush_color's stay at -1 and %false is returned.  If any pwq
 * has in flight commands, its pwq->flush_color is set to
 * @flush_color, @wq->nr_pwqs_to_flush is updated accordingly, pwq
 * wakeup logic is armed and %true is returned.
 *
 * The caller should have initialized @wq->first_flusher prior to
 * calling this function with non-negative @flush_color.  If
 * @flush_color is negative, no flush color update is done and %false
 * is returned.
 *
 * If @work_color is non-negative, all pwqs should have the same
 * work_color which is previous to @work_color and all will be
 * advanced to @work_color.
 *
 * CONTEXT:
 * mutex_lock(wq->mutex).
 *
 * Return:
 * %true if @flush_color >= 0 and there's something to flush.  %false
 * otherwise.
 */
static bool flush_workqueue_prep_pwqs(struct workqueue_struct *wq,
				      int flush_color, int work_color)
{
	bool wait = false;
	struct pool_workqueue *pwq;
	struct worker_pool *current_pool = NULL;

	if (flush_color >= 0) {
		WARN_ON_ONCE(atomic_read(&wq->nr_pwqs_to_flush));
		atomic_set(&wq->nr_pwqs_to_flush, 1);
	}

	/*
	 * For unbound workqueue, pwqs will map to only a few pools.
	 * Most of the time, pwqs within the same pool will be linked
	 * sequentially to wq->pwqs by cpu index. So in the majority
	 * of pwq iters, the pool is the same, only doing lock/unlock
	 * if the pool has changed. This can largely reduce expensive
	 * lock operations.
	 */
	for_each_pwq(pwq, wq) {
		if (current_pool != pwq->pool) {
			if (likely(current_pool))
				raw_spin_unlock_irq(&current_pool->lock);
			current_pool = pwq->pool;
			raw_spin_lock_irq(&current_pool->lock);
		}

		if (flush_color >= 0) {
			WARN_ON_ONCE(pwq->flush_color != -1);

			if (pwq->nr_in_flight[flush_color]) {
				pwq->flush_color = flush_color;
				atomic_inc(&wq->nr_pwqs_to_flush);
				wait = true;
			}
		}

		if (work_color >= 0) {
			WARN_ON_ONCE(work_color != work_next_color(pwq->work_color));
			pwq->work_color = work_color;
		}

	}

	if (current_pool)
		raw_spin_unlock_irq(&current_pool->lock);

	if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_pwqs_to_flush))
		complete(&wq->first_flusher->done);

	return wait;
}

static void touch_wq_lockdep_map(struct workqueue_struct *wq)
{
#ifdef CONFIG_LOCKDEP
	if (unlikely(!wq->lockdep_map))
		return;

	if (wq->flags & WQ_BH)
		local_bh_disable();

	lock_map_acquire(wq->lockdep_map);
	lock_map_release(wq->lockdep_map);

	if (wq->flags & WQ_BH)
		local_bh_enable();
#endif
}

static void touch_work_lockdep_map(struct work_struct *work,
				   struct workqueue_struct *wq)
{
#ifdef CONFIG_LOCKDEP
	if (wq->flags & WQ_BH)
		local_bh_disable();

	lock_map_acquire(&work->lockdep_map);
	lock_map_release(&work->lockdep_map);

	if (wq->flags & WQ_BH)
		local_bh_enable();
#endif
}

/**
 * __flush_workqueue - ensure that any scheduled work has run to completion.
 * @wq: workqueue to flush
 *
 * This function sleeps until all work items which were queued on entry
 * have finished execution, but it is not livelocked by new incoming ones.
 */
void __flush_workqueue(struct workqueue_struct *wq)
{
	struct wq_flusher this_flusher = {
		.list = LIST_HEAD_INIT(this_flusher.list),
		.flush_color = -1,
		.done = COMPLETION_INITIALIZER_ONSTACK_MAP(this_flusher.done, (*wq->lockdep_map)),
	};
	int next_color;

	if (WARN_ON(!wq_online))
		return;

	touch_wq_lockdep_map(wq);

	mutex_lock(&wq->mutex);

	/*
	 * Start-to-wait phase
	 */
	next_color = work_next_color(wq->work_color);

	if (next_color != wq->flush_color) {
		/*
		 * Color space is not full.  The current work_color
		 * becomes our flush_color and work_color is advanced
		 * by one.
		 */
		WARN_ON_ONCE(!list_empty(&wq->flusher_overflow));
		this_flusher.flush_color = wq->work_color;
		wq->work_color = next_color;

		if (!wq->first_flusher) {
			/* no flush in progress, become the first flusher */
			WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);

			wq->first_flusher = &this_flusher;

			if (!flush_workqueue_prep_pwqs(wq, wq->flush_color,
						       wq->work_color)) {
				/* nothing to flush, done */
				wq->flush_color = next_color;
				wq->first_flusher = NULL;
				goto out_unlock;
			}
		} else {
			/* wait in queue */
			WARN_ON_ONCE(wq->flush_color == this_flusher.flush_color);
			list_add_tail(&this_flusher.list, &wq->flusher_queue);
			flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
		}
	} else {
		/*
		 * Oops, color space is full, wait on overflow queue.
		 * The next flush completion will assign us
		 * flush_color and transfer to flusher_queue.
		 */
		list_add_tail(&this_flusher.list, &wq->flusher_overflow);
	}

	check_flush_dependency(wq, NULL, false);

	mutex_unlock(&wq->mutex);

	wait_for_completion(&this_flusher.done);

	/*
	 * Wake-up-and-cascade phase
	 *
	 * First flushers are responsible for cascading flushes and
	 * handling overflow.  Non-first flushers can simply return.
	 */
	if (READ_ONCE(wq->first_flusher) != &this_flusher)
		return;

	mutex_lock(&wq->mutex);

	/* we might have raced, check again with mutex held */
	if (wq->first_flusher != &this_flusher)
		goto out_unlock;

	WRITE_ONCE(wq->first_flusher, NULL);

	WARN_ON_ONCE(!list_empty(&this_flusher.list));
	WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color);

	while (true) {
		struct wq_flusher *next, *tmp;

		/* complete all the flushers sharing the current flush color */
		list_for_each_entry_safe(next, tmp, &wq->flusher_queue, list) {
			if (next->flush_color != wq->flush_color)
				break;
			list_del_init(&next->list);
			complete(&next->done);
		}

		WARN_ON_ONCE(!list_empty(&wq->flusher_overflow) &&
			     wq->flush_color != work_next_color(wq->work_color));

		/* this flush_color is finished, advance by one */
		wq->flush_color = work_next_color(wq->flush_color);

		/* one color has been freed, handle overflow queue */
		if (!list_empty(&wq->flusher_overflow)) {
			/*
			 * Assign the same color to all overflowed
			 * flushers, advance work_color and append to
			 * flusher_queue.  This is the start-to-wait
			 * phase for these overflowed flushers.
			 */
			list_for_each_entry(tmp, &wq->flusher_overflow, list)
				tmp->flush_color = wq->work_color;

			wq->work_color = work_next_color(wq->work_color);

			list_splice_tail_init(&wq->flusher_overflow,
					      &wq->flusher_queue);
			flush_workqueue_prep_pwqs(wq, -1, wq->work_color);
		}

		if (list_empty(&wq->flusher_queue)) {
			WARN_ON_ONCE(wq->flush_color != wq->work_color);
			break;
		}

		/*
		 * Need to flush more colors.  Make the next flusher
		 * the new first flusher and arm pwqs.
		 */
		WARN_ON_ONCE(wq->flush_color == wq->work_color);
		WARN_ON_ONCE(wq->flush_color != next->flush_color);

		list_del_init(&next->list);
		wq->first_flusher = next;

		if (flush_workqueue_prep_pwqs(wq, wq->flush_color, -1))
			break;

		/*
		 * Meh... this color is already done, clear first
		 * flusher and repeat cascading.
		 */
		wq->first_flusher = NULL;
	}

out_unlock:
	mutex_unlock(&wq->mutex);
}
EXPORT_SYMBOL(__flush_workqueue);

/**
 * drain_workqueue - drain a workqueue
 * @wq: workqueue to drain
 *
 * Wait until the workqueue becomes empty.  While draining is in progress,
 * only chain queueing is allowed.  IOW, only currently pending or running
 * work items on @wq can queue further work items on it.  @wq is flushed
 * repeatedly until it becomes empty.  The number of flushing is determined
 * by the depth of chaining and should be relatively short.  Whine if it
 * takes too long.
 */
void drain_workqueue(struct workqueue_struct *wq)
{
	unsigned int flush_cnt = 0;
	struct pool_workqueue *pwq;

	/*
	 * __queue_work() needs to test whether there are drainers, is much
	 * hotter than drain_workqueue() and already looks at @wq->flags.
	 * Use __WQ_DRAINING so that queue doesn't have to check nr_drainers.
	 */
	mutex_lock(&wq->mutex);
	if (!wq->nr_drainers++)
		wq->flags |= __WQ_DRAINING;
	mutex_unlock(&wq->mutex);
reflush:
	__flush_workqueue(wq);

	mutex_lock(&wq->mutex);

	for_each_pwq(pwq, wq) {
		bool drained;

		raw_spin_lock_irq(&pwq->pool->lock);
		drained = pwq_is_empty(pwq);
		raw_spin_unlock_irq(&pwq->pool->lock);

		if (drained)
			continue;

		if (++flush_cnt == 10 ||
		    (flush_cnt % 100 == 0 && flush_cnt <= 1000))
			pr_warn("workqueue %s: %s() isn't complete after %u tries\n",
				wq->name, __func__, flush_cnt);

		mutex_unlock(&wq->mutex);
		goto reflush;
	}

	if (!--wq->nr_drainers)
		wq->flags &= ~__WQ_DRAINING;
	mutex_unlock(&wq->mutex);
}
EXPORT_SYMBOL_GPL(drain_workqueue);

static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
			     bool from_cancel)
{
	struct worker *worker = NULL;
	struct worker_pool *pool;
	struct pool_workqueue *pwq;
	struct workqueue_struct *wq;

	rcu_read_lock();
	pool = get_work_pool(work);
	if (!pool) {
		rcu_read_unlock();
		return false;
	}

	raw_spin_lock_irq(&pool->lock);
	/* see the comment in try_to_grab_pending() with the same code */
	pwq = get_work_pwq(work);
	if (pwq) {
		if (unlikely(pwq->pool != pool))
			goto already_gone;
	} else {
		worker = find_worker_executing_work(pool, work);
		if (!worker)
			goto already_gone;
		pwq = worker->current_pwq;
	}

	wq = pwq->wq;
	check_flush_dependency(wq, work, from_cancel);

	insert_wq_barrier(pwq, barr, work, worker);
	raw_spin_unlock_irq(&pool->lock);

	touch_work_lockdep_map(work, wq);

	/*
	 * Force a lock recursion deadlock when using flush_work() inside a
	 * single-threaded or rescuer equipped workqueue.
	 *
	 * For single threaded workqueues the deadlock happens when the work
	 * is after the work issuing the flush_work(). For rescuer equipped
	 * workqueues the deadlock happens when the rescuer stalls, blocking
	 * forward progress.
	 */
	if (!from_cancel && (wq->saved_max_active == 1 || wq->rescuer))
		touch_wq_lockdep_map(wq);

	rcu_read_unlock();
	return true;
already_gone:
	raw_spin_unlock_irq(&pool->lock);
	rcu_read_unlock();
	return false;
}

static bool __flush_work(struct work_struct *work, bool from_cancel)
{
	struct wq_barrier barr;

	if (WARN_ON(!wq_online))
		return false;

	if (WARN_ON(!work->func))
		return false;

	if (!start_flush_work(work, &barr, from_cancel))
		return false;

	/*
	 * start_flush_work() returned %true. If @from_cancel is set, we know
	 * that @work must have been executing during start_flush_work() and
	 * can't currently be queued. Its data must contain OFFQ bits. If @work
	 * was queued on a BH workqueue, we also know that it was running in the
	 * BH context and thus can be busy-waited.
	 */
	if (from_cancel) {
		unsigned long data = *work_data_bits(work);

		if (!WARN_ON_ONCE(data & WORK_STRUCT_PWQ) &&
		    (data & WORK_OFFQ_BH)) {
			/*
			 * On RT, prevent a live lock when %current preempted
			 * soft interrupt processing by blocking on lock which
			 * is owned by the thread invoking the callback.
			 */
			while (!try_wait_for_completion(&barr.done)) {
				if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
					struct worker_pool *pool;

					guard(rcu)();
					pool = get_work_pool(work);
					if (pool)
						workqueue_callback_cancel_wait_running(pool);
				} else {
					cpu_relax();
				}
			}
			goto out_destroy;
		}
	}

	wait_for_completion(&barr.done);

out_destroy:
	destroy_work_on_stack(&barr.work);
	return true;
}

/**
 * flush_work - wait for a work to finish executing the last queueing instance
 * @work: the work to flush
 *
 * Wait until @work has finished execution.  @work is guaranteed to be idle
 * on return if it hasn't been requeued since flush started.
 *
 * Return:
 * %true if flush_work() waited for the work to finish execution,
 * %false if it was already idle.
 */
bool flush_work(struct work_struct *work)
{
	might_sleep();
	return __flush_work(work, false);
}
EXPORT_SYMBOL_GPL(flush_work);

/**
 * flush_delayed_work - wait for a dwork to finish executing the last queueing
 * @dwork: the delayed work to flush
 *
 * Delayed timer is cancelled and the pending work is queued for
 * immediate execution.  Like flush_work(), this function only
 * considers the last queueing instance of @dwork.
 *
 * Return:
 * %true if flush_work() waited for the work to finish execution,
 * %false if it was already idle.
 */
bool flush_delayed_work(struct delayed_work *dwork)
{
	local_irq_disable();
	if (timer_delete_sync(&dwork->timer))
		__queue_work(dwork->cpu, dwork->wq, &dwork->work);
	local_irq_enable();
	return flush_work(&dwork->work);
}
EXPORT_SYMBOL(flush_delayed_work);

/**
 * flush_rcu_work - wait for a rwork to finish executing the last queueing
 * @rwork: the rcu work to flush
 *
 * Return:
 * %true if flush_rcu_work() waited for the work to finish execution,
 * %false if it was already idle.
 */
bool flush_rcu_work(struct rcu_work *rwork)
{
	if (test_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&rwork->work))) {
		rcu_barrier();
		flush_work(&rwork->work);
		return true;
	} else {
		return flush_work(&rwork->work);
	}
}
EXPORT_SYMBOL(flush_rcu_work);

static void work_offqd_disable(struct work_offq_data *offqd)
{
	const unsigned long max = (1lu << WORK_OFFQ_DISABLE_BITS) - 1;

	if (likely(offqd->disable < max))
		offqd->disable++;
	else
		WARN_ONCE(true, "workqueue: work disable count overflowed\n");
}

static void work_offqd_enable(struct work_offq_data *offqd)
{
	if (likely(offqd->disable > 0))
		offqd->disable--;
	else
		WARN_ONCE(true, "workqueue: work disable count underflowed\n");
}

static bool __cancel_work(struct work_struct *work, u32 cflags)
{
	struct work_offq_data offqd;
	unsigned long irq_flags;
	int ret;

	ret = work_grab_pending(work, cflags, &irq_flags);

	work_offqd_unpack(&offqd, *work_data_bits(work));

	if (cflags & WORK_CANCEL_DISABLE)
		work_offqd_disable(&offqd);

	set_work_pool_and_clear_pending(work, offqd.pool_id,
					work_offqd_pack_flags(&offqd));
	local_irq_restore(irq_flags);
	return ret;
}

static bool __cancel_work_sync(struct work_struct *work, u32 cflags)
{
	bool ret;

	ret = __cancel_work(work, cflags | WORK_CANCEL_DISABLE);

	if (*work_data_bits(work) & WORK_OFFQ_BH)
		WARN_ON_ONCE(in_hardirq());
	else
		might_sleep();

	/*
	 * Skip __flush_work() during early boot when we know that @work isn't
	 * executing. This allows canceling during early boot.
	 */
	if (wq_online)
		__flush_work(work, true);

	if (!(cflags & WORK_CANCEL_DISABLE))
		enable_work(work);

	return ret;
}

/*
 * See cancel_delayed_work()
 */
bool cancel_work(struct work_struct *work)
{
	return __cancel_work(work, 0);
}
EXPORT_SYMBOL(cancel_work);

/**
 * cancel_work_sync - cancel a work and wait for it to finish
 * @work: the work to cancel
 *
 * Cancel @work and wait for its execution to finish. This function can be used
 * even if the work re-queues itself or migrates to another workqueue. On return
 * from this function, @work is guaranteed to be not pending or executing on any
 * CPU as long as there aren't racing enqueues.
 *
 * cancel_work_sync(&delayed_work->work) must not be used for delayed_work's.
 * Use cancel_delayed_work_sync() instead.
 *
 * Must be called from a sleepable context if @work was last queued on a non-BH
 * workqueue. Can also be called from non-hardirq atomic contexts including BH
 * if @work was last queued on a BH workqueue.
 *
 * Returns %true if @work was pending, %false otherwise.
 */
bool cancel_work_sync(struct work_struct *work)
{
	return __cancel_work_sync(work, 0);
}
EXPORT_SYMBOL_GPL(cancel_work_sync);

/**
 * cancel_delayed_work - cancel a delayed work
 * @dwork: delayed_work to cancel
 *
 * Kill off a pending delayed_work.
 *
 * Return: %true if @dwork was pending and canceled; %false if it wasn't
 * pending.
 *
 * Note:
 * The work callback function may still be running on return, unless
 * it returns %true and the work doesn't re-arm itself.  Explicitly flush or
 * use cancel_delayed_work_sync() to wait on it.
 *
 * This function is safe to call from any context including IRQ handler.
 */
bool cancel_delayed_work(struct delayed_work *dwork)
{
	return __cancel_work(&dwork->work, WORK_CANCEL_DELAYED);
}
EXPORT_SYMBOL(cancel_delayed_work);

/**
 * cancel_delayed_work_sync - cancel a delayed work and wait for it to finish
 * @dwork: the delayed work cancel
 *
 * This is cancel_work_sync() for delayed works.
 *
 * Return:
 * %true if @dwork was pending, %false otherwise.
 */
bool cancel_delayed_work_sync(struct delayed_work *dwork)
{
	return __cancel_work_sync(&dwork->work, WORK_CANCEL_DELAYED);
}
EXPORT_SYMBOL(cancel_delayed_work_sync);

/**
 * disable_work - Disable and cancel a work item
 * @work: work item to disable
 *
 * Disable @work by incrementing its disable count and cancel it if currently
 * pending. As long as the disable count is non-zero, any attempt to queue @work
 * will fail and return %false. The maximum supported disable depth is 2 to the
 * power of %WORK_OFFQ_DISABLE_BITS, currently 65536.
 *
 * Can be called from any context. Returns %true if @work was pending, %false
 * otherwise.
 */
bool disable_work(struct work_struct *work)
{
	return __cancel_work(work, WORK_CANCEL_DISABLE);
}
EXPORT_SYMBOL_GPL(disable_work);

/**
 * disable_work_sync - Disable, cancel and drain a work item
 * @work: work item to disable
 *
 * Similar to disable_work() but also wait for @work to finish if currently
 * executing.
 *
 * Must be called from a sleepable context if @work was last queued on a non-BH
 * workqueue. Can also be called from non-hardirq atomic contexts including BH
 * if @work was last queued on a BH workqueue.
 *
 * Returns %true if @work was pending, %false otherwise.
 */
bool disable_work_sync(struct work_struct *work)
{
	return __cancel_work_sync(work, WORK_CANCEL_DISABLE);
}
EXPORT_SYMBOL_GPL(disable_work_sync);

/**
 * enable_work - Enable a work item
 * @work: work item to enable
 *
 * Undo disable_work[_sync]() by decrementing @work's disable count. @work can
 * only be queued if its disable count is 0.
 *
 * Can be called from any context. Returns %true if the disable count reached 0.
 * Otherwise, %false.
 */
bool enable_work(struct work_struct *work)
{
	struct work_offq_data offqd;
	unsigned long irq_flags;

	work_grab_pending(work, 0, &irq_flags);

	work_offqd_unpack(&offqd, *work_data_bits(work));
	work_offqd_enable(&offqd);
	set_work_pool_and_clear_pending(work, offqd.pool_id,
					work_offqd_pack_flags(&offqd));
	local_irq_restore(irq_flags);

	return !offqd.disable;
}
EXPORT_SYMBOL_GPL(enable_work);

/**
 * disable_delayed_work - Disable and cancel a delayed work item
 * @dwork: delayed work item to disable
 *
 * disable_work() for delayed work items.
 */
bool disable_delayed_work(struct delayed_work *dwork)
{
	return __cancel_work(&dwork->work,
			     WORK_CANCEL_DELAYED | WORK_CANCEL_DISABLE);
}
EXPORT_SYMBOL_GPL(disable_delayed_work);

/**
 * disable_delayed_work_sync - Disable, cancel and drain a delayed work item
 * @dwork: delayed work item to disable
 *
 * disable_work_sync() for delayed work items.
 */
bool disable_delayed_work_sync(struct delayed_work *dwork)
{
	return __cancel_work_sync(&dwork->work,
				  WORK_CANCEL_DELAYED | WORK_CANCEL_DISABLE);
}
EXPORT_SYMBOL_GPL(disable_delayed_work_sync);

/**
 * enable_delayed_work - Enable a delayed work item
 * @dwork: delayed work item to enable
 *
 * enable_work() for delayed work items.
 */
bool enable_delayed_work(struct delayed_work *dwork)
{
	return enable_work(&dwork->work);
}
EXPORT_SYMBOL_GPL(enable_delayed_work);

/**
 * schedule_on_each_cpu - execute a function synchronously on each online CPU
 * @func: the function to call
 *
 * schedule_on_each_cpu() executes @func on each online CPU using the
 * system workqueue and blocks until all CPUs have completed.
 * schedule_on_each_cpu() is very slow.
 *
 * Return:
 * 0 on success, -errno on failure.
 */
int schedule_on_each_cpu(work_func_t func)
{
	int cpu;
	struct work_struct __percpu *works;

	works = alloc_percpu(struct work_struct);
	if (!works)
		return -ENOMEM;

	cpus_read_lock();

	for_each_online_cpu(cpu) {
		struct work_struct *work = per_cpu_ptr(works, cpu);

		INIT_WORK(work, func);
		schedule_work_on(cpu, work);
	}

	for_each_online_cpu(cpu)
		flush_work(per_cpu_ptr(works, cpu));

	cpus_read_unlock();
	free_percpu(works);
	return 0;
}

/**
 * execute_in_process_context - reliably execute the routine with user context
 * @fn:		the function to execute
 * @ew:		guaranteed storage for the execute work structure (must
 *		be available when the work executes)
 *
 * Executes the function immediately if process context is available,
 * otherwise schedules the function for delayed execution.
 *
 * Return:	0 - function was executed
 *		1 - function was scheduled for execution
 */
int execute_in_process_context(work_func_t fn, struct execute_work *ew)
{
	if (!in_interrupt()) {
		fn(&ew->work);
		return 0;
	}

	INIT_WORK(&ew->work, fn);
	schedule_work(&ew->work);

	return 1;
}
EXPORT_SYMBOL_GPL(execute_in_process_context);

/**
 * free_workqueue_attrs - free a workqueue_attrs
 * @attrs: workqueue_attrs to free
 *
 * Undo alloc_workqueue_attrs().
 */
void free_workqueue_attrs(struct workqueue_attrs *attrs)
{
	if (attrs) {
		free_cpumask_var(attrs->cpumask);
		free_cpumask_var(attrs->__pod_cpumask);
		kfree(attrs);
	}
}

/**
 * alloc_workqueue_attrs - allocate a workqueue_attrs
 *
 * Allocate a new workqueue_attrs, initialize with default settings and
 * return it.
 *
 * Return: The allocated new workqueue_attr on success. %NULL on failure.
 */
struct workqueue_attrs *alloc_workqueue_attrs_noprof(void)
{
	struct workqueue_attrs *attrs;

	attrs = kzalloc_obj(*attrs);
	if (!attrs)
		goto fail;
	if (!alloc_cpumask_var(&attrs->cpumask, GFP_KERNEL))
		goto fail;
	if (!alloc_cpumask_var(&attrs->__pod_cpumask, GFP_KERNEL))
		goto fail;

	cpumask_copy(attrs->cpumask, cpu_possible_mask);
	attrs->affn_scope = WQ_AFFN_DFL;
	return attrs;
fail:
	free_workqueue_attrs(attrs);
	return NULL;
}

static void copy_workqueue_attrs(struct workqueue_attrs *to,
				 const struct workqueue_attrs *from)
{
	to->nice = from->nice;
	cpumask_copy(to->cpumask, from->cpumask);
	cpumask_copy(to->__pod_cpumask, from->__pod_cpumask);
	to->affn_strict = from->affn_strict;

	/*
	 * Unlike hash and equality test, copying shouldn't ignore wq-only
	 * fields as copying is used for both pool and wq attrs. Instead,
	 * get_unbound_pool() explicitly clears the fields.
	 */
	to->affn_scope = from->affn_scope;
	to->ordered = from->ordered;
}

/*
 * Some attrs fields are workqueue-only. Clear them for worker_pool's. See the
 * comments in 'struct workqueue_attrs' definition.
 */
static void wqattrs_clear_for_pool(struct workqueue_attrs *attrs)
{
	attrs->affn_scope = WQ_AFFN_NR_TYPES;
	attrs->ordered = false;
	if (attrs->affn_strict)
		cpumask_copy(attrs->cpumask, cpu_possible_mask);
}

/* hash value of the content of @attr */
static u32 wqattrs_hash(const struct workqueue_attrs *attrs)
{
	u32 hash = 0;

	hash = jhash_1word(attrs->nice, hash);
	hash = jhash_1word(attrs->affn_strict, hash);
	hash = jhash(cpumask_bits(attrs->__pod_cpumask),
		     BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash);
	if (!attrs->affn_strict)
		hash = jhash(cpumask_bits(attrs->cpumask),
			     BITS_TO_LONGS(nr_cpumask_bits) * sizeof(long), hash);
	return hash;
}

/* content equality test */
static bool wqattrs_equal(const struct workqueue_attrs *a,
			  const struct workqueue_attrs *b)
{
	if (a->nice != b->nice)
		return false;
	if (a->affn_strict != b->affn_strict)
		return false;
	if (!cpumask_equal(a->__pod_cpumask, b->__pod_cpumask))
		return false;
	if (!a->affn_strict && !cpumask_equal(a->cpumask, b->cpumask))
		return false;
	return true;
}

/* Update @attrs with actually available CPUs */
static void wqattrs_actualize_cpumask(struct workqueue_attrs *attrs,
				      const cpumask_t *unbound_cpumask)
{
	/*
	 * Calculate the effective CPU mask of @attrs given @unbound_cpumask. If
	 * @attrs->cpumask doesn't overlap with @unbound_cpumask, we fallback to
	 * @unbound_cpumask.
	 */
	cpumask_and(attrs->cpumask, attrs->cpumask, unbound_cpumask);
	if (unlikely(cpumask_empty(attrs->cpumask)))
		cpumask_copy(attrs->cpumask, unbound_cpumask);
}

/* find wq_pod_type to use for @attrs */
static const struct wq_pod_type *
wqattrs_pod_type(const struct workqueue_attrs *attrs)
{
	enum wq_affn_scope scope;
	struct wq_pod_type *pt;

	/* to synchronize access to wq_affn_dfl */
	lockdep_assert_held(&wq_pool_mutex);

	if (attrs->affn_scope == WQ_AFFN_DFL)
		scope = wq_affn_dfl;
	else
		scope = attrs->affn_scope;

	pt = &wq_pod_types[scope];

	if (!WARN_ON_ONCE(attrs->affn_scope == WQ_AFFN_NR_TYPES) &&
	    likely(pt->nr_pods))
		return pt;

	/*
	 * Before workqueue_init_topology(), only SYSTEM is available which is
	 * initialized in workqueue_init_early().
	 */
	pt = &wq_pod_types[WQ_AFFN_SYSTEM];
	BUG_ON(!pt->nr_pods);
	return pt;
}

/**
 * init_worker_pool - initialize a newly zalloc'd worker_pool
 * @pool: worker_pool to initialize
 *
 * Initialize a newly zalloc'd @pool.  It also allocates @pool->attrs.
 *
 * Return: 0 on success, -errno on failure.  Even on failure, all fields
 * inside @pool proper are initialized and put_unbound_pool() can be called
 * on @pool safely to release it.
 */
static int init_worker_pool(struct worker_pool *pool)
{
	raw_spin_lock_init(&pool->lock);
	pool->id = -1;
	pool->cpu = -1;
	pool->node = NUMA_NO_NODE;
	pool->flags |= POOL_DISASSOCIATED;
	pool->last_progress_ts = jiffies;
	INIT_LIST_HEAD(&pool->worklist);
	INIT_LIST_HEAD(&pool->idle_list);
	hash_init(pool->busy_hash);

	timer_setup(&pool->idle_timer, idle_worker_timeout, TIMER_DEFERRABLE);
	INIT_WORK(&pool->idle_cull_work, idle_cull_fn);

	timer_setup(&pool->mayday_timer, pool_mayday_timeout, 0);

	INIT_LIST_HEAD(&pool->workers);

	ida_init(&pool->worker_ida);
	INIT_HLIST_NODE(&pool->hash_node);
	pool->refcnt = 1;
#ifdef CONFIG_PREEMPT_RT
	spin_lock_init(&pool->cb_lock);
#endif

	/* shouldn't fail above this point */
	pool->attrs = alloc_workqueue_attrs();
	if (!pool->attrs)
		return -ENOMEM;

	wqattrs_clear_for_pool(pool->attrs);

	return 0;
}

#ifdef CONFIG_LOCKDEP
static void wq_init_lockdep(struct workqueue_struct *wq)
{
	char *lock_name;

	lockdep_register_key(&wq->key);
	lock_name = kasprintf(GFP_KERNEL, "%s%s", "(wq_completion)", wq->name);
	if (!lock_name)
		lock_name = wq->name;

	wq->lock_name = lock_name;
	wq->lockdep_map = &wq->__lockdep_map;
	lockdep_init_map(wq->lockdep_map, lock_name, &wq->key, 0);
}

static void wq_unregister_lockdep(struct workqueue_struct *wq)
{
	if (wq->lockdep_map != &wq->__lockdep_map)
		return;

	lockdep_unregister_key(&wq->key);
}

static void wq_free_lockdep(struct workqueue_struct *wq)
{
	if (wq->lockdep_map != &wq->__lockdep_map)
		return;

	if (wq->lock_name != wq->name)
		kfree(wq->lock_name);
}
#else
static void wq_init_lockdep(struct workqueue_struct *wq)
{
}

static void wq_unregister_lockdep(struct workqueue_struct *wq)
{
}

static void wq_free_lockdep(struct workqueue_struct *wq)
{
}
#endif

static void free_node_nr_active(struct wq_node_nr_active **nna_ar)
{
	int node;

	for_each_node(node) {
		kfree(nna_ar[node]);
		nna_ar[node] = NULL;
	}

	kfree(nna_ar[nr_node_ids]);
	nna_ar[nr_node_ids] = NULL;
}

static void init_node_nr_active(struct wq_node_nr_active *nna)
{
	nna->max = WQ_DFL_MIN_ACTIVE;
	atomic_set(&nna->nr, 0);
	raw_spin_lock_init(&nna->lock);
	INIT_LIST_HEAD(&nna->pending_pwqs);
}

/*
 * Each node's nr_active counter will be accessed mostly from its own node and
 * should be allocated in the node.
 */
static int alloc_node_nr_active(struct wq_node_nr_active **nna_ar)
{
	struct wq_node_nr_active *nna;
	int node;

	for_each_node(node) {
		nna = kzalloc_node(sizeof(*nna), GFP_KERNEL, node);
		if (!nna)
			goto err_free;
		init_node_nr_active(nna);
		nna_ar[node] = nna;
	}

	/* [nr_node_ids] is used as the fallback */
	nna = kzalloc_node(sizeof(*nna), GFP_KERNEL, NUMA_NO_NODE);
	if (!nna)
		goto err_free;
	init_node_nr_active(nna);
	nna_ar[nr_node_ids] = nna;

	return 0;

err_free:
	free_node_nr_active(nna_ar);
	return -ENOMEM;
}

static void rcu_free_wq(struct rcu_head *rcu)
{
	struct workqueue_struct *wq =
		container_of(rcu, struct workqueue_struct, rcu);

	if (wq->flags & WQ_UNBOUND)
		free_node_nr_active(wq->node_nr_active);

	wq_free_lockdep(wq);
	free_percpu(wq->cpu_pwq);
	free_workqueue_attrs(wq->unbound_attrs);
	kfree(wq);
}

static void rcu_free_pool(struct rcu_head *rcu)
{
	struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);

	ida_destroy(&pool->worker_ida);
	free_workqueue_attrs(pool->attrs);
	kfree(pool);
}

/**
 * put_unbound_pool - put a worker_pool
 * @pool: worker_pool to put
 *
 * Put @pool.  If its refcnt reaches zero, it gets destroyed in RCU
 * safe manner.  get_unbound_pool() calls this function on its failure path
 * and this function should be able to release pools which went through,
 * successfully or not, init_worker_pool().
 *
 * Should be called with wq_pool_mutex held.
 */
static void put_unbound_pool(struct worker_pool *pool)
{
	struct worker *worker;
	LIST_HEAD(cull_list);

	lockdep_assert_held(&wq_pool_mutex);

	if (--pool->refcnt)
		return;

	/* sanity checks */
	if (WARN_ON(!(pool->cpu < 0)) ||
	    WARN_ON(!list_empty(&pool->worklist)))
		return;

	/* release id and unhash */
	if (pool->id >= 0)
		idr_remove(&worker_pool_idr, pool->id);
	hash_del(&pool->hash_node);

	/*
	 * Become the manager and destroy all workers.  This prevents
	 * @pool's workers from blocking on attach_mutex.  We're the last
	 * manager and @pool gets freed with the flag set.
	 *
	 * Having a concurrent manager is quite unlikely to happen as we can
	 * only get here with
	 *   pwq->refcnt == pool->refcnt == 0
	 * which implies no work queued to the pool, which implies no worker can
	 * become the manager. However a worker could have taken the role of
	 * manager before the refcnts dropped to 0, since maybe_create_worker()
	 * drops pool->lock
	 */
	while (true) {
		rcuwait_wait_event(&manager_wait,
				   !(pool->flags & POOL_MANAGER_ACTIVE),
				   TASK_UNINTERRUPTIBLE);

		mutex_lock(&wq_pool_attach_mutex);
		raw_spin_lock_irq(&pool->lock);
		if (!(pool->flags & POOL_MANAGER_ACTIVE)) {
			pool->flags |= POOL_MANAGER_ACTIVE;
			break;
		}
		raw_spin_unlock_irq(&pool->lock);
		mutex_unlock(&wq_pool_attach_mutex);
	}

	while ((worker = first_idle_worker(pool)))
		set_worker_dying(worker, &cull_list);
	WARN_ON(pool->nr_workers || pool->nr_idle);
	raw_spin_unlock_irq(&pool->lock);

	detach_dying_workers(&cull_list);

	mutex_unlock(&wq_pool_attach_mutex);

	reap_dying_workers(&cull_list);

	/* shut down the timers */
	timer_delete_sync(&pool->idle_timer);
	cancel_work_sync(&pool->idle_cull_work);
	timer_delete_sync(&pool->mayday_timer);

	/* RCU protected to allow dereferences from get_work_pool() */
	call_rcu(&pool->rcu, rcu_free_pool);
}

/**
 * get_unbound_pool - get a worker_pool with the specified attributes
 * @attrs: the attributes of the worker_pool to get
 *
 * Obtain a worker_pool which has the same attributes as @attrs, bump the
 * reference count and return it.  If there already is a matching
 * worker_pool, it will be used; otherwise, this function attempts to
 * create a new one.
 *
 * Should be called with wq_pool_mutex held.
 *
 * Return: On success, a worker_pool with the same attributes as @attrs.
 * On failure, %NULL.
 */
static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
{
	struct wq_pod_type *pt = &wq_pod_types[WQ_AFFN_NUMA];
	u32 hash = wqattrs_hash(attrs);
	struct worker_pool *pool;
	int pod, node = NUMA_NO_NODE;

	lockdep_assert_held(&wq_pool_mutex);

	/* do we already have a matching pool? */
	hash_for_each_possible(unbound_pool_hash, pool, hash_node, hash) {
		if (wqattrs_equal(pool->attrs, attrs)) {
			pool->refcnt++;
			return pool;
		}
	}

	/* If __pod_cpumask is contained inside a NUMA pod, that's our node */
	for (pod = 0; pod < pt->nr_pods; pod++) {
		if (cpumask_subset(attrs->__pod_cpumask, pt->pod_cpus[pod])) {
			node = pt->pod_node[pod];
			break;
		}
	}

	/* nope, create a new one */
	pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, node);
	if (!pool || init_worker_pool(pool) < 0)
		goto fail;

	pool->node = node;
	copy_workqueue_attrs(pool->attrs, attrs);
	wqattrs_clear_for_pool(pool->attrs);

	if (worker_pool_assign_id(pool) < 0)
		goto fail;

	/* create and start the initial worker */
	if (wq_online && !create_worker(pool))
		goto fail;

	/* install */
	hash_add(unbound_pool_hash, &pool->hash_node, hash);

	return pool;
fail:
	if (pool)
		put_unbound_pool(pool);
	return NULL;
}

/*
 * Scheduled on pwq_release_worker by put_pwq() when an unbound pwq hits zero
 * refcnt and needs to be destroyed.
 */
static void pwq_release_workfn(struct kthread_work *work)
{
	struct pool_workqueue *pwq = container_of(work, struct pool_workqueue,
						  release_work);
	struct workqueue_struct *wq = pwq->wq;
	struct worker_pool *pool = pwq->pool;
	bool is_last = false;

	/*
	 * When @pwq is not linked, it doesn't hold any reference to the
	 * @wq, and @wq is invalid to access.
	 */
	if (!list_empty(&pwq->pwqs_node)) {
		mutex_lock(&wq->mutex);
		list_del_rcu(&pwq->pwqs_node);
		is_last = list_empty(&wq->pwqs);

		/*
		 * For ordered workqueue with a plugged dfl_pwq, restart it now.
		 */
		if (!is_last && (wq->flags & __WQ_ORDERED))
			unplug_oldest_pwq(wq);

		mutex_unlock(&wq->mutex);
	}

	if (wq->flags & WQ_UNBOUND) {
		mutex_lock(&wq_pool_mutex);
		put_unbound_pool(pool);
		mutex_unlock(&wq_pool_mutex);
	}

	if (!list_empty(&pwq->pending_node)) {
		struct wq_node_nr_active *nna =
			wq_node_nr_active(pwq->wq, pwq->pool->node);

		raw_spin_lock_irq(&nna->lock);
		list_del_init(&pwq->pending_node);
		raw_spin_unlock_irq(&nna->lock);
	}

	kfree_rcu(pwq, rcu);

	/*
	 * If we're the last pwq going away, @wq is already dead and no one
	 * is gonna access it anymore.  Schedule RCU free.
	 */
	if (is_last) {
		wq_unregister_lockdep(wq);
		call_rcu(&wq->rcu, rcu_free_wq);
	}
}

/* initialize newly allocated @pwq which is associated with @wq and @pool */
static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
		     struct worker_pool *pool)
{
	BUG_ON((unsigned long)pwq & ~WORK_STRUCT_PWQ_MASK);

	memset(pwq, 0, sizeof(*pwq));

	pwq->pool = pool;
	pwq->wq = wq;
	pwq->flush_color = -1;
	pwq->refcnt = 1;
	INIT_LIST_HEAD(&pwq->inactive_works);
	INIT_LIST_HEAD(&pwq->pending_node);
	INIT_LIST_HEAD(&pwq->pwqs_node);
	INIT_LIST_HEAD(&pwq->mayday_node);
	kthread_init_work(&pwq->release_work, pwq_release_workfn);

	/*
	 * Set the dummy cursor work with valid function and get_work_pwq().
	 *
	 * The cursor work should only be in the pwq->pool->worklist, and
	 * should not be treated as a processable work item.
	 *
	 * WORK_STRUCT_PENDING and WORK_STRUCT_INACTIVE just make it less
	 * surprise for kernel debugging tools and reviewers.
	 */
	INIT_WORK(&pwq->mayday_cursor, mayday_cursor_func);
	atomic_long_set(&pwq->mayday_cursor.data, (unsigned long)pwq |
			WORK_STRUCT_PENDING | WORK_STRUCT_PWQ | WORK_STRUCT_INACTIVE);
}

/* sync @pwq with the current state of its associated wq and link it */
static void link_pwq(struct pool_workqueue *pwq)
{
	struct workqueue_struct *wq = pwq->wq;

	lockdep_assert_held(&wq->mutex);

	/* may be called multiple times, ignore if already linked */
	if (!list_empty(&pwq->pwqs_node))
		return;

	/* set the matching work_color */
	pwq->work_color = wq->work_color;

	/* link in @pwq */
	list_add_tail_rcu(&pwq->pwqs_node, &wq->pwqs);
}

/* obtain a pool matching @attr and create a pwq associating the pool and @wq */
static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
					const struct workqueue_attrs *attrs)
{
	struct worker_pool *pool;
	struct pool_workqueue *pwq;

	lockdep_assert_held(&wq_pool_mutex);

	pool = get_unbound_pool(attrs);
	if (!pool)
		return NULL;

	pwq = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL, pool->node);
	if (!pwq) {
		put_unbound_pool(pool);
		return NULL;
	}

	init_pwq(pwq, wq, pool);
	return pwq;
}

static void apply_wqattrs_lock(void)
{
	mutex_lock(&wq_pool_mutex);
}

static void apply_wqattrs_unlock(void)
{
	mutex_unlock(&wq_pool_mutex);
}

/**
 * wq_calc_pod_cpumask - calculate a wq_attrs' cpumask for a pod
 * @attrs: the wq_attrs of the default pwq of the target workqueue
 * @cpu: the target CPU
 *
 * Calculate the cpumask a workqueue with @attrs should use on @pod.
 * The result is stored in @attrs->__pod_cpumask.
 *
 * If pod affinity is not enabled, @attrs->cpumask is always used. If enabled
 * and @pod has online CPUs requested by @attrs, the returned cpumask is the
 * intersection of the possible CPUs of @pod and @attrs->cpumask.
 *
 * The caller is responsible for ensuring that the cpumask of @pod stays stable.
 */
static void wq_calc_pod_cpumask(struct workqueue_attrs *attrs, int cpu)
{
	const struct wq_pod_type *pt = wqattrs_pod_type(attrs);
	int pod = pt->cpu_pod[cpu];

	/* calculate possible CPUs in @pod that @attrs wants */
	cpumask_and(attrs->__pod_cpumask, pt->pod_cpus[pod], attrs->cpumask);
	/* does @pod have any online CPUs @attrs wants? */
	if (!cpumask_intersects(attrs->__pod_cpumask, wq_online_cpumask)) {
		cpumask_copy(attrs->__pod_cpumask, attrs->cpumask);
		return;
	}
}

/* install @pwq into @wq and return the old pwq, @cpu < 0 for dfl_pwq */
static struct pool_workqueue *install_unbound_pwq(struct workqueue_struct *wq,
					int cpu, struct pool_workqueue *pwq)
{
	struct pool_workqueue __rcu **slot = unbound_pwq_slot(wq, cpu);
	struct pool_workqueue *old_pwq;

	lockdep_assert_held(&wq_pool_mutex);
	lockdep_assert_held(&wq->mutex);

	/* link_pwq() can handle duplicate calls */
	link_pwq(pwq);

	old_pwq = rcu_access_pointer(*slot);
	rcu_assign_pointer(*slot, pwq);
	return old_pwq;
}

/* context to store the prepared attrs & pwqs before applying */
struct apply_wqattrs_ctx {
	struct workqueue_struct	*wq;		/* target workqueue */
	struct workqueue_attrs	*attrs;		/* attrs to apply */
	struct list_head	list;		/* queued for batching commit */
	struct pool_workqueue	*dfl_pwq;
	struct pool_workqueue	*pwq_tbl[];
};

/* free the resources after success or abort */
static void apply_wqattrs_cleanup(struct apply_wqattrs_ctx *ctx)
{
	if (ctx) {
		int cpu;

		for_each_possible_cpu(cpu)
			put_pwq_unlocked(ctx->pwq_tbl[cpu]);
		put_pwq_unlocked(ctx->dfl_pwq);

		free_workqueue_attrs(ctx->attrs);

		kfree(ctx);
	}
}

/* allocate the attrs and pwqs for later installation */
static struct apply_wqattrs_ctx *
apply_wqattrs_prepare(struct workqueue_struct *wq,
		      const struct workqueue_attrs *attrs,
		      const cpumask_var_t unbound_cpumask)
{
	struct apply_wqattrs_ctx *ctx;
	struct workqueue_attrs *new_attrs;
	int cpu;

	lockdep_assert_held(&wq_pool_mutex);

	if (WARN_ON(attrs->affn_scope < 0 ||
		    attrs->affn_scope >= WQ_AFFN_NR_TYPES))
		return ERR_PTR(-EINVAL);

	ctx = kzalloc_flex(*ctx, pwq_tbl, nr_cpu_ids);

	new_attrs = alloc_workqueue_attrs();
	if (!ctx || !new_attrs)
		goto out_free;

	/*
	 * If something goes wrong during CPU up/down, we'll fall back to
	 * the default pwq covering whole @attrs->cpumask.  Always create
	 * it even if we don't use it immediately.
	 */
	copy_workqueue_attrs(new_attrs, attrs);
	wqattrs_actualize_cpumask(new_attrs, unbound_cpumask);
	cpumask_copy(new_attrs->__pod_cpumask, new_attrs->cpumask);
	ctx->dfl_pwq = alloc_unbound_pwq(wq, new_attrs);
	if (!ctx->dfl_pwq)
		goto out_free;

	for_each_possible_cpu(cpu) {
		if (new_attrs->ordered) {
			ctx->dfl_pwq->refcnt++;
			ctx->pwq_tbl[cpu] = ctx->dfl_pwq;
		} else {
			wq_calc_pod_cpumask(new_attrs, cpu);
			ctx->pwq_tbl[cpu] = alloc_unbound_pwq(wq, new_attrs);
			if (!ctx->pwq_tbl[cpu])
				goto out_free;
		}
	}

	/* save the user configured attrs and sanitize it. */
	copy_workqueue_attrs(new_attrs, attrs);
	cpumask_and(new_attrs->cpumask, new_attrs->cpumask, cpu_possible_mask);
	cpumask_copy(new_attrs->__pod_cpumask, new_attrs->cpumask);
	ctx->attrs = new_attrs;

	/*
	 * For initialized ordered workqueues, there should only be one pwq
	 * (dfl_pwq). Set the plugged flag of ctx->dfl_pwq to suspend execution
	 * of newly queued work items until execution of older work items in
	 * the old pwq's have completed.
	 */
	if ((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs))
		ctx->dfl_pwq->plugged = true;

	ctx->wq = wq;
	return ctx;

out_free:
	free_workqueue_attrs(new_attrs);
	apply_wqattrs_cleanup(ctx);
	return ERR_PTR(-ENOMEM);
}

/* set attrs and install prepared pwqs, @ctx points to old pwqs on return */
static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
{
	int cpu;

	/* all pwqs have been created successfully, let's install'em */
	mutex_lock(&ctx->wq->mutex);

	copy_workqueue_attrs(ctx->wq->unbound_attrs, ctx->attrs);

	/* save the previous pwqs and install the new ones */
	for_each_possible_cpu(cpu)
		ctx->pwq_tbl[cpu] = install_unbound_pwq(ctx->wq, cpu,
							ctx->pwq_tbl[cpu]);
	ctx->dfl_pwq = install_unbound_pwq(ctx->wq, -1, ctx->dfl_pwq);

	/* update node_nr_active->max */
	wq_update_node_max_active(ctx->wq, -1);

	mutex_unlock(&ctx->wq->mutex);
}

static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
					const struct workqueue_attrs *attrs)
{
	struct apply_wqattrs_ctx *ctx;

	/* only unbound workqueues can change attributes */
	if (WARN_ON(!(wq->flags & WQ_UNBOUND)))
		return -EINVAL;

	ctx = apply_wqattrs_prepare(wq, attrs, wq_unbound_cpumask);
	if (IS_ERR(ctx))
		return PTR_ERR(ctx);

	/* the ctx has been prepared successfully, let's commit it */
	apply_wqattrs_commit(ctx);
	apply_wqattrs_cleanup(ctx);

	return 0;
}

/**
 * apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue
 * @wq: the target workqueue
 * @attrs: the workqueue_attrs to apply, allocated with alloc_workqueue_attrs()
 *
 * Apply @attrs to an unbound workqueue @wq. Unless disabled, this function maps
 * a separate pwq to each CPU pod with possibles CPUs in @attrs->cpumask so that
 * work items are affine to the pod it was issued on. Older pwqs are released as
 * in-flight work items finish. Note that a work item which repeatedly requeues
 * itself back-to-back will stay on its current pwq.
 *
 * Performs GFP_KERNEL allocations.
 *
 * Return: 0 on success and -errno on failure.
 */
int apply_workqueue_attrs(struct workqueue_struct *wq,
			  const struct workqueue_attrs *attrs)
{
	int ret;

	mutex_lock(&wq_pool_mutex);
	ret = apply_workqueue_attrs_locked(wq, attrs);
	mutex_unlock(&wq_pool_mutex);

	return ret;
}

/**
 * unbound_wq_update_pwq - update a pwq slot for CPU hot[un]plug
 * @wq: the target workqueue
 * @cpu: the CPU to update the pwq slot for
 *
 * This function is to be called from %CPU_DOWN_PREPARE, %CPU_ONLINE and
 * %CPU_DOWN_FAILED.  @cpu is in the same pod of the CPU being hot[un]plugged.
 *
 *
 * If pod affinity can't be adjusted due to memory allocation failure, it falls
 * back to @wq->dfl_pwq which may not be optimal but is always correct.
 *
 * Note that when the last allowed CPU of a pod goes offline for a workqueue
 * with a cpumask spanning multiple pods, the workers which were already
 * executing the work items for the workqueue will lose their CPU affinity and
 * may execute on any CPU. This is similar to how per-cpu workqueues behave on
 * CPU_DOWN. If a workqueue user wants strict affinity, it's the user's
 * responsibility to flush the work item from CPU_DOWN_PREPARE.
 */
static void unbound_wq_update_pwq(struct workqueue_struct *wq, int cpu)
{
	struct pool_workqueue *old_pwq = NULL, *pwq;
	struct workqueue_attrs *target_attrs;

	lockdep_assert_held(&wq_pool_mutex);

	if (!(wq->flags & WQ_UNBOUND) || wq->unbound_attrs->ordered)
		return;

	/*
	 * We don't wanna alloc/free wq_attrs for each wq for each CPU.
	 * Let's use a preallocated one.  The following buf is protected by
	 * CPU hotplug exclusion.
	 */
	target_attrs = unbound_wq_update_pwq_attrs_buf;

	copy_workqueue_attrs(target_attrs, wq->unbound_attrs);
	wqattrs_actualize_cpumask(target_attrs, wq_unbound_cpumask);

	/* nothing to do if the target cpumask matches the current pwq */
	wq_calc_pod_cpumask(target_attrs, cpu);
	if (wqattrs_equal(target_attrs, unbound_pwq(wq, cpu)->pool->attrs))
		return;

	/* create a new pwq */
	pwq = alloc_unbound_pwq(wq, target_attrs);
	if (!pwq) {
		pr_warn("workqueue: allocation failed while updating CPU pod affinity of \"%s\"\n",
			wq->name);
		goto use_dfl_pwq;
	}

	/* Install the new pwq. */
	mutex_lock(&wq->mutex);
	old_pwq = install_unbound_pwq(wq, cpu, pwq);
	goto out_unlock;

use_dfl_pwq:
	mutex_lock(&wq->mutex);
	pwq = unbound_pwq(wq, -1);
	raw_spin_lock_irq(&pwq->pool->lock);
	get_pwq(pwq);
	raw_spin_unlock_irq(&pwq->pool->lock);
	old_pwq = install_unbound_pwq(wq, cpu, pwq);
out_unlock:
	mutex_unlock(&wq->mutex);
	put_pwq_unlocked(old_pwq);
}

static int alloc_and_link_pwqs(struct workqueue_struct *wq)
{
	bool highpri = wq->flags & WQ_HIGHPRI;
	int cpu, ret;

	lockdep_assert_held(&wq_pool_mutex);

	wq->cpu_pwq = alloc_percpu(struct pool_workqueue *);
	if (!wq->cpu_pwq)
		goto enomem;

	if (!(wq->flags & WQ_UNBOUND)) {
		struct worker_pool __percpu *pools;

		if (wq->flags & WQ_BH)
			pools = bh_worker_pools;
		else
			pools = cpu_worker_pools;

		for_each_possible_cpu(cpu) {
			struct pool_workqueue **pwq_p;
			struct worker_pool *pool;

			pool = &(per_cpu_ptr(pools, cpu)[highpri]);
			pwq_p = per_cpu_ptr(wq->cpu_pwq, cpu);

			*pwq_p = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL,
						       pool->node);
			if (!*pwq_p)
				goto enomem;

			init_pwq(*pwq_p, wq, pool);

			mutex_lock(&wq->mutex);
			link_pwq(*pwq_p);
			mutex_unlock(&wq->mutex);
		}
		return 0;
	}

	if (wq->flags & __WQ_ORDERED) {
		struct pool_workqueue *dfl_pwq;

		ret = apply_workqueue_attrs_locked(wq, ordered_wq_attrs[highpri]);
		/* there should only be single pwq for ordering guarantee */
		dfl_pwq = rcu_access_pointer(wq->dfl_pwq);
		WARN(!ret && (wq->pwqs.next != &dfl_pwq->pwqs_node ||
			      wq->pwqs.prev != &dfl_pwq->pwqs_node),
		     "ordering guarantee broken for workqueue %s\n", wq->name);
	} else {
		ret = apply_workqueue_attrs_locked(wq, unbound_std_wq_attrs[highpri]);
	}

	if (ret)
		goto enomem;
	return 0;

enomem:
	if (wq->cpu_pwq) {
		for_each_possible_cpu(cpu) {
			struct pool_workqueue *pwq = *per_cpu_ptr(wq->cpu_pwq, cpu);

			if (pwq) {
				/*
				 * Unlink pwq from wq->pwqs since link_pwq()
				 * may have already added it. wq->mutex is not
				 * needed as the wq has not been published yet.
				 */
				if (!list_empty(&pwq->pwqs_node))
					list_del_rcu(&pwq->pwqs_node);
				kmem_cache_free(pwq_cache, pwq);
			}
		}
		free_percpu(wq->cpu_pwq);
		wq->cpu_pwq = NULL;
	}
	return -ENOMEM;
}

static int wq_clamp_max_active(int max_active, unsigned int flags,
			       const char *name)
{
	if (max_active < 1 || max_active > WQ_MAX_ACTIVE)
		pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
			max_active, name, 1, WQ_MAX_ACTIVE);

	return clamp_val(max_active, 1, WQ_MAX_ACTIVE);
}

/*
 * Workqueues which may be used during memory reclaim should have a rescuer
 * to guarantee forward progress.
 */
static int init_rescuer(struct workqueue_struct *wq)
{
	struct worker *rescuer;
	char id_buf[WORKER_ID_LEN];
	int ret;

	lockdep_assert_held(&wq_pool_mutex);

	if (!(wq->flags & WQ_MEM_RECLAIM))
		return 0;

	rescuer = alloc_worker(NUMA_NO_NODE);
	if (!rescuer) {
		pr_err("workqueue: Failed to allocate a rescuer for wq \"%s\"\n",
		       wq->name);
		return -ENOMEM;
	}

	rescuer->rescue_wq = wq;
	format_worker_id(id_buf, sizeof(id_buf), rescuer, NULL);

	rescuer->task = kthread_create(rescuer_thread, rescuer, "%s", id_buf);
	if (IS_ERR(rescuer->task)) {
		ret = PTR_ERR(rescuer->task);
		pr_err("workqueue: Failed to create a rescuer kthread for wq \"%s\": %pe",
		       wq->name, ERR_PTR(ret));
		kfree(rescuer);
		return ret;
	}

	wq->rescuer = rescuer;

	/* initial cpumask is consistent with the detached rescuer and unbind_worker() */
	if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask))
		kthread_bind_mask(rescuer->task, wq_unbound_cpumask);
	else
		kthread_bind_mask(rescuer->task, cpu_possible_mask);

	wake_up_process(rescuer->task);

	return 0;
}

/**
 * wq_adjust_max_active - update a wq's max_active to the current setting
 * @wq: target workqueue
 *
 * If @wq isn't freezing, set @wq->max_active to the saved_max_active and
 * activate inactive work items accordingly. If @wq is freezing, clear
 * @wq->max_active to zero.
 */
static void wq_adjust_max_active(struct workqueue_struct *wq)
{
	bool activated;
	int new_max, new_min;

	lockdep_assert_held(&wq->mutex);

	if ((wq->flags & WQ_FREEZABLE) && workqueue_freezing) {
		new_max = 0;
		new_min = 0;
	} else {
		new_max = wq->saved_max_active;
		new_min = wq->saved_min_active;
	}

	if (wq->max_active == new_max && wq->min_active == new_min)
		return;

	/*
	 * Update @wq->max/min_active and then kick inactive work items if more
	 * active work items are allowed. This doesn't break work item ordering
	 * because new work items are always queued behind existing inactive
	 * work items if there are any.
	 */
	WRITE_ONCE(wq->max_active, new_max);
	WRITE_ONCE(wq->min_active, new_min);

	if (wq->flags & WQ_UNBOUND)
		wq_update_node_max_active(wq, -1);

	if (new_max == 0)
		return;

	/*
	 * Round-robin through pwq's activating the first inactive work item
	 * until max_active is filled.
	 */
	do {
		struct pool_workqueue *pwq;

		activated = false;
		for_each_pwq(pwq, wq) {
			unsigned long irq_flags;

			/* can be called during early boot w/ irq disabled */
			raw_spin_lock_irqsave(&pwq->pool->lock, irq_flags);
			if (pwq_activate_first_inactive(pwq, true)) {
				activated = true;
				kick_pool(pwq->pool);
			}
			raw_spin_unlock_irqrestore(&pwq->pool->lock, irq_flags);
		}
	} while (activated);
}

__printf(1, 0)
static struct workqueue_struct *__alloc_workqueue(const char *fmt,
						  unsigned int flags,
						  int max_active, va_list args)
{
	struct workqueue_struct *wq;
	size_t wq_size;
	int name_len;

	if (flags & WQ_BH) {
		if (WARN_ON_ONCE(flags & ~__WQ_BH_ALLOWS))
			return NULL;
		if (WARN_ON_ONCE(max_active))
			return NULL;
	}

	/* see the comment above the definition of WQ_POWER_EFFICIENT */
	if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
		flags |= WQ_UNBOUND;

	/* allocate wq and format name */
	if (flags & WQ_UNBOUND)
		wq_size = struct_size(wq, node_nr_active, nr_node_ids + 1);
	else
		wq_size = sizeof(*wq);

	wq = kzalloc_noprof(wq_size, GFP_KERNEL);
	if (!wq)
		return NULL;

	if (flags & WQ_UNBOUND) {
		wq->unbound_attrs = alloc_workqueue_attrs_noprof();
		if (!wq->unbound_attrs)
			goto err_free_wq;
	}

	name_len = vsnprintf(wq->name, sizeof(wq->name), fmt, args);

	if (name_len >= WQ_NAME_LEN)
		pr_warn_once("workqueue: name exceeds WQ_NAME_LEN. Truncating to: %s\n",
			     wq->name);

	if (flags & WQ_BH) {
		/*
		 * BH workqueues always share a single execution context per CPU
		 * and don't impose any max_active limit.
		 */
		max_active = INT_MAX;
	} else {
		max_active = max_active ?: WQ_DFL_ACTIVE;
		max_active = wq_clamp_max_active(max_active, flags, wq->name);
	}

	/* init wq */
	wq->flags = flags;
	wq->max_active = max_active;
	wq->min_active = min(max_active, WQ_DFL_MIN_ACTIVE);
	wq->saved_max_active = wq->max_active;
	wq->saved_min_active = wq->min_active;
	mutex_init(&wq->mutex);
	atomic_set(&wq->nr_pwqs_to_flush, 0);
	INIT_LIST_HEAD(&wq->pwqs);
	INIT_LIST_HEAD(&wq->flusher_queue);
	INIT_LIST_HEAD(&wq->flusher_overflow);
	INIT_LIST_HEAD(&wq->maydays);

	INIT_LIST_HEAD(&wq->list);

	if (flags & WQ_UNBOUND) {
		if (alloc_node_nr_active(wq->node_nr_active) < 0)
			goto err_free_wq;
	}

	/*
	 * wq_pool_mutex protects the workqueues list, allocations of PWQs,
	 * and the global freeze state.
	 */
	apply_wqattrs_lock();

	if (alloc_and_link_pwqs(wq) < 0)
		goto err_unlock_free_node_nr_active;

	mutex_lock(&wq->mutex);
	wq_adjust_max_active(wq);
	mutex_unlock(&wq->mutex);

	list_add_tail_rcu(&wq->list, &workqueues);

	if (wq_online && init_rescuer(wq) < 0)
		goto err_unlock_destroy;

	apply_wqattrs_unlock();

	if ((wq->flags & WQ_SYSFS) && workqueue_sysfs_register(wq))
		goto err_destroy;

	return wq;

err_unlock_free_node_nr_active:
	apply_wqattrs_unlock();
	/*
	 * Failed alloc_and_link_pwqs() may leave pending pwq->release_work,
	 * flushing the pwq_release_worker ensures that the pwq_release_workfn()
	 * completes before calling kfree(wq).
	 */
	if (wq->flags & WQ_UNBOUND) {
		kthread_flush_worker(pwq_release_worker);
		free_node_nr_active(wq->node_nr_active);
	}
err_free_wq:
	free_workqueue_attrs(wq->unbound_attrs);
	kfree(wq);
	return NULL;
err_unlock_destroy:
	apply_wqattrs_unlock();
err_destroy:
	destroy_workqueue(wq);
	return NULL;
}

__printf(1, 0)
static struct workqueue_struct *alloc_workqueue_va(const char *fmt,
						   unsigned int flags,
						   int max_active,
						   va_list args)
{
	struct workqueue_struct *wq;

	wq = __alloc_workqueue(fmt, flags, max_active, args);
	if (wq)
		wq_init_lockdep(wq);

	return wq;
}

__printf(1, 4)
struct workqueue_struct *alloc_workqueue_noprof(const char *fmt,
						unsigned int flags,
						int max_active, ...)
{
	struct workqueue_struct *wq;
	va_list args;

	va_start(args, max_active);
	wq = alloc_workqueue_va(fmt, flags, max_active, args);
	va_end(args);

	return wq;
}
EXPORT_SYMBOL_GPL(alloc_workqueue_noprof);

static void devm_workqueue_release(void *res)
{
	destroy_workqueue(res);
}

__printf(2, 5) struct workqueue_struct *
devm_alloc_workqueue_noprof(struct device *dev, const char *fmt,
			    unsigned int flags, int max_active, ...)
{
	struct workqueue_struct *wq;
	va_list args;
	int ret;

	va_start(args, max_active);
	wq = alloc_workqueue_va(fmt, flags, max_active, args);
	va_end(args);
	if (!wq)
		return NULL;

	ret = devm_add_action_or_reset(dev, devm_workqueue_release, wq);
	if (ret)
		return NULL;

	return wq;
}
EXPORT_SYMBOL_GPL(devm_alloc_workqueue_noprof);

#ifdef CONFIG_LOCKDEP
__printf(1, 5)
struct workqueue_struct *
alloc_workqueue_lockdep_map(const char *fmt, unsigned int flags,
			    int max_active, struct lockdep_map *lockdep_map, ...)
{
	struct workqueue_struct *wq;
	va_list args;

	va_start(args, lockdep_map);
	wq = __alloc_workqueue(fmt, flags, max_active, args);
	va_end(args);
	if (!wq)
		return NULL;

	wq->lockdep_map = lockdep_map;

	return wq;
}
EXPORT_SYMBOL_GPL(alloc_workqueue_lockdep_map);
#endif

static bool pwq_busy(struct pool_workqueue *pwq)
{
	int i;

	for (i = 0; i < WORK_NR_COLORS; i++)
		if (pwq->nr_in_flight[i])
			return true;

	if ((pwq != rcu_access_pointer(pwq->wq->dfl_pwq)) && (pwq->refcnt > 1))
		return true;
	if (!pwq_is_empty(pwq))
		return true;

	return false;
}

/**
 * destroy_workqueue - safely terminate a workqueue
 * @wq: target workqueue
 *
 * Safely destroy a workqueue. All work currently pending will be done first.
 *
 * This function does NOT guarantee that non-pending work that has been
 * submitted with queue_delayed_work() and similar functions will be done
 * before destroying the workqueue. The fundamental problem is that, currently,
 * the workqueue has no way of accessing non-pending delayed_work. delayed_work
 * is only linked on the timer-side. All delayed_work must, therefore, be
 * canceled before calling this function.
 *
 * TODO: It would be better if the problem described above wouldn't exist and
 * destroy_workqueue() would cleanly cancel all pending and non-pending
 * delayed_work.
 */
void destroy_workqueue(struct workqueue_struct *wq)
{
	struct pool_workqueue *pwq;
	int cpu;

	/*
	 * Remove it from sysfs first so that sanity check failure doesn't
	 * lead to sysfs name conflicts.
	 */
	workqueue_sysfs_unregister(wq);

	/* mark the workqueue destruction is in progress */
	mutex_lock(&wq->mutex);
	wq->flags |= __WQ_DESTROYING;
	mutex_unlock(&wq->mutex);

	/* drain it before proceeding with destruction */
	drain_workqueue(wq);

	/* kill rescuer, if sanity checks fail, leave it w/o rescuer */
	if (wq->rescuer) {
		/* rescuer will empty maydays list before exiting */
		kthread_stop(wq->rescuer->task);
		kfree(wq->rescuer);
		wq->rescuer = NULL;
	}

	/*
	 * Sanity checks - grab all the locks so that we wait for all
	 * in-flight operations which may do put_pwq().
	 */
	mutex_lock(&wq_pool_mutex);
	mutex_lock(&wq->mutex);
	for_each_pwq(pwq, wq) {
		raw_spin_lock_irq(&pwq->pool->lock);
		if (WARN_ON(pwq_busy(pwq))) {
			pr_warn("%s: %s has the following busy pwq\n",
				__func__, wq->name);
			show_pwq(pwq);
			raw_spin_unlock_irq(&pwq->pool->lock);
			mutex_unlock(&wq->mutex);
			mutex_unlock(&wq_pool_mutex);
			show_one_workqueue(wq);
			return;
		}
		raw_spin_unlock_irq(&pwq->pool->lock);
	}
	mutex_unlock(&wq->mutex);

	/*
	 * wq list is used to freeze wq, remove from list after
	 * flushing is complete in case freeze races us.
	 */
	list_del_rcu(&wq->list);
	mutex_unlock(&wq_pool_mutex);

	/*
	 * We're the sole accessor of @wq. Directly access cpu_pwq and dfl_pwq
	 * to put the base refs. @wq will be auto-destroyed from the last
	 * pwq_put. RCU read lock prevents @wq from going away from under us.
	 */
	rcu_read_lock();

	for_each_possible_cpu(cpu) {
		put_pwq_unlocked(unbound_pwq(wq, cpu));
		RCU_INIT_POINTER(*unbound_pwq_slot(wq, cpu), NULL);
	}

	put_pwq_unlocked(unbound_pwq(wq, -1));
	RCU_INIT_POINTER(*unbound_pwq_slot(wq, -1), NULL);

	rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(destroy_workqueue);

/**
 * workqueue_set_max_active - adjust max_active of a workqueue
 * @wq: target workqueue
 * @max_active: new max_active value.
 *
 * Set max_active of @wq to @max_active. See the alloc_workqueue() function
 * comment.
 *
 * CONTEXT:
 * Don't call from IRQ context.
 */
void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
{
	/* max_active doesn't mean anything for BH workqueues */
	if (WARN_ON(wq->flags & WQ_BH))
		return;
	/* disallow meddling with max_active for ordered workqueues */
	if (WARN_ON(wq->flags & __WQ_ORDERED))
		return;

	max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);

	mutex_lock(&wq->mutex);

	wq->saved_max_active = max_active;
	if (wq->flags & WQ_UNBOUND)
		wq->saved_min_active = min(wq->saved_min_active, max_active);

	wq_adjust_max_active(wq);

	mutex_unlock(&wq->mutex);
}
EXPORT_SYMBOL_GPL(workqueue_set_max_active);

/**
 * workqueue_set_min_active - adjust min_active of an unbound workqueue
 * @wq: target unbound workqueue
 * @min_active: new min_active value
 *
 * Set min_active of an unbound workqueue. Unlike other types of workqueues, an
 * unbound workqueue is not guaranteed to be able to process max_active
 * interdependent work items. Instead, an unbound workqueue is guaranteed to be
 * able to process min_active number of interdependent work items which is
 * %WQ_DFL_MIN_ACTIVE by default.
 *
 * Use this function to adjust the min_active value between 0 and the current
 * max_active.
 */
void workqueue_set_min_active(struct workqueue_struct *wq, int min_active)
{
	/* min_active is only meaningful for non-ordered unbound workqueues */
	if (WARN_ON((wq->flags & (WQ_BH | WQ_UNBOUND | __WQ_ORDERED)) !=
		    WQ_UNBOUND))
		return;

	mutex_lock(&wq->mutex);
	wq->saved_min_active = clamp(min_active, 0, wq->saved_max_active);
	wq_adjust_max_active(wq);
	mutex_unlock(&wq->mutex);
}

/**
 * current_work - retrieve %current task's work struct
 *
 * Determine if %current task is a workqueue worker and what it's working on.
 * Useful to find out the context that the %current task is running in.
 *
 * Return: work struct if %current task is a workqueue worker, %NULL otherwise.
 */
struct work_struct *current_work(void)
{
	struct worker *worker = current_wq_worker();

	return worker ? worker->current_work : NULL;
}
EXPORT_SYMBOL(current_work);

/**
 * current_is_workqueue_rescuer - is %current workqueue rescuer?
 *
 * Determine whether %current is a workqueue rescuer.  Can be used from
 * work functions to determine whether it's being run off the rescuer task.
 *
 * Return: %true if %current is a workqueue rescuer. %false otherwise.
 */
bool current_is_workqueue_rescuer(void)
{
	struct worker *worker = current_wq_worker();

	return worker && worker->rescue_wq;
}

/**
 * workqueue_congested - test whether a workqueue is congested
 * @cpu: CPU in question
 * @wq: target workqueue
 *
 * Test whether @wq's cpu workqueue for @cpu is congested.  There is
 * no synchronization around this function and the test result is
 * unreliable and only useful as advisory hints or for debugging.
 *
 * If @cpu is WORK_CPU_UNBOUND, the test is performed on the local CPU.
 *
 * With the exception of ordered workqueues, all workqueues have per-cpu
 * pool_workqueues, each with its own congested state. A workqueue being
 * congested on one CPU doesn't mean that the workqueue is contested on any
 * other CPUs.
 *
 * Return:
 * %true if congested, %false otherwise.
 */
bool workqueue_congested(int cpu, struct workqueue_struct *wq)
{
	struct pool_workqueue *pwq;
	bool ret;

	preempt_disable();

	if (cpu == WORK_CPU_UNBOUND)
		cpu = smp_processor_id();

	pwq = *per_cpu_ptr(wq->cpu_pwq, cpu);
	ret = !list_empty(&pwq->inactive_works);

	preempt_enable();

	return ret;
}
EXPORT_SYMBOL_GPL(workqueue_congested);

/**
 * work_busy - test whether a work is currently pending or running
 * @work: the work to be tested
 *
 * Test whether @work is currently pending or running.  There is no
 * synchronization around this function and the test result is
 * unreliable and only useful as advisory hints or for debugging.
 *
 * Return:
 * OR'd bitmask of WORK_BUSY_* bits.
 */
unsigned int work_busy(struct work_struct *work)
{
	struct worker_pool *pool;
	unsigned long irq_flags;
	unsigned int ret = 0;

	if (work_pending(work))
		ret |= WORK_BUSY_PENDING;

	rcu_read_lock();
	pool = get_work_pool(work);
	if (pool) {
		raw_spin_lock_irqsave(&pool->lock, irq_flags);
		if (find_worker_executing_work(pool, work))
			ret |= WORK_BUSY_RUNNING;
		raw_spin_unlock_irqrestore(&pool->lock, irq_flags);
	}
	rcu_read_unlock();

	return ret;
}
EXPORT_SYMBOL_GPL(work_busy);

/**
 * set_worker_desc - set description for the current work item
 * @fmt: printf-style format string
 * @...: arguments for the format string
 *
 * This function can be called by a running work function to describe what
 * the work item is about.  If the worker task gets dumped, this
 * information will be printed out together to help debugging.  The
 * description can be at most WORKER_DESC_LEN including the trailing '\0'.
 */
void set_worker_desc(const char *fmt, ...)
{
	struct worker *worker = current_wq_worker();
	va_list args;

	if (worker) {
		va_start(args, fmt);
		vsnprintf(worker->desc, sizeof(worker->desc), fmt, args);
		va_end(args);
	}
}
EXPORT_SYMBOL_GPL(set_worker_desc);

/**
 * print_worker_info - print out worker information and description
 * @log_lvl: the log level to use when printing
 * @task: target task
 *
 * If @task is a worker and currently executing a work item, print out the
 * name of the workqueue being serviced and worker description set with
 * set_worker_desc() by the currently executing work item.
 *
 * This function can be safely called on any task as long as the
 * task_struct itself is accessible.  While safe, this function isn't
 * synchronized and may print out mixups or garbages of limited length.
 */
void print_worker_info(const char *log_lvl, struct task_struct *task)
{
	work_func_t *fn = NULL;
	char name[WQ_NAME_LEN] = { };
	char desc[WORKER_DESC_LEN] = { };
	struct pool_workqueue *pwq = NULL;
	struct workqueue_struct *wq = NULL;
	struct worker *worker;

	if (!(task->flags & PF_WQ_WORKER))
		return;

	/*
	 * This function is called without any synchronization and @task
	 * could be in any state.  Be careful with dereferences.
	 */
	worker = kthread_probe_data(task);

	/*
	 * Carefully copy the associated workqueue's workfn, name and desc.
	 * Keep the original last '\0' in case the original is garbage.
	 */
	copy_from_kernel_nofault(&fn, &worker->current_func, sizeof(fn));
	copy_from_kernel_nofault(&pwq, &worker->current_pwq, sizeof(pwq));
	copy_from_kernel_nofault(&wq, &pwq->wq, sizeof(wq));
	copy_from_kernel_nofault(name, wq->name, sizeof(name) - 1);
	copy_from_kernel_nofault(desc, worker->desc, sizeof(desc) - 1);

	if (fn || name[0] || desc[0]) {
		printk("%sWorkqueue: %s %ps", log_lvl, name, fn);
		if (strcmp(name, desc))
			pr_cont(" (%s)", desc);
		pr_cont("\n");
	}
}

static void pr_cont_pool_info(struct worker_pool *pool)
{
	pr_cont(" cpus=%*pbl", nr_cpumask_bits, pool->attrs->cpumask);
	if (pool->node != NUMA_NO_NODE)
		pr_cont(" node=%d", pool->node);
	pr_cont(" flags=0x%x", pool->flags);
	if (pool->flags & POOL_BH)
		pr_cont(" bh%s",
			pool->attrs->nice == HIGHPRI_NICE_LEVEL ? "-hi" : "");
	else
		pr_cont(" nice=%d", pool->attrs->nice);
}

static void pr_cont_worker_id(struct worker *worker)
{
	struct worker_pool *pool = worker->pool;

	if (pool->flags & POOL_BH)
		pr_cont("bh%s",
			pool->attrs->nice == HIGHPRI_NICE_LEVEL ? "-hi" : "");
	else
		pr_cont("%d%s", task_pid_nr(worker->task),
			worker->rescue_wq ? "(RESCUER)" : "");
}

struct pr_cont_work_struct {
	bool comma;
	work_func_t func;
	long ctr;
};

static void pr_cont_work_flush(bool comma, work_func_t func, struct pr_cont_work_struct *pcwsp)
{
	if (!pcwsp->ctr)
		goto out_record;
	if (func == pcwsp->func) {
		pcwsp->ctr++;
		return;
	}
	if (pcwsp->ctr == 1)
		pr_cont("%s %ps", pcwsp->comma ? "," : "", pcwsp->func);
	else
		pr_cont("%s %ld*%ps", pcwsp->comma ? "," : "", pcwsp->ctr, pcwsp->func);
	pcwsp->ctr = 0;
out_record:
	if ((long)func == -1L)
		return;
	pcwsp->comma = comma;
	pcwsp->func = func;
	pcwsp->ctr = 1;
}

static void pr_cont_work(bool comma, struct work_struct *work, struct pr_cont_work_struct *pcwsp)
{
	if (work->func == wq_barrier_func) {
		struct wq_barrier *barr;

		barr = container_of(work, struct wq_barrier, work);

		pr_cont_work_flush(comma, (work_func_t)-1, pcwsp);
		pr_cont("%s BAR(%d)", comma ? "," : "",
			task_pid_nr(barr->task));
	} else {
		if (!comma)
			pr_cont_work_flush(comma, (work_func_t)-1, pcwsp);
		pr_cont_work_flush(comma, work->func, pcwsp);
	}
}

static void show_pwq(struct pool_workqueue *pwq)
{
	struct pr_cont_work_struct pcws = { .ctr = 0, };
	struct worker_pool *pool = pwq->pool;
	struct work_struct *work;
	struct worker *worker;
	bool has_in_flight = false, has_pending = false;
	int bkt;

	pr_info("  pwq %d:", pool->id);
	pr_cont_pool_info(pool);

	pr_cont(" active=%d refcnt=%d%s\n",
		pwq->nr_active, pwq->refcnt,
		!list_empty(&pwq->mayday_node) ? " MAYDAY" : "");

	hash_for_each(pool->busy_hash, bkt, worker, hentry) {
		if (worker->current_pwq == pwq) {
			has_in_flight = true;
			break;
		}
	}
	if (has_in_flight) {
		bool comma = false;

		pr_info("    in-flight:");
		hash_for_each(pool->busy_hash, bkt, worker, hentry) {
			if (worker->current_pwq != pwq)
				continue;

			pr_cont(" %s", comma ? "," : "");
			pr_cont_worker_id(worker);
			pr_cont(":%ps", worker->current_func);
			pr_cont(" for %us",
				jiffies_to_msecs(jiffies - worker->current_start) / 1000);
			list_for_each_entry(work, &worker->scheduled, entry)
				pr_cont_work(false, work, &pcws);
			pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
			comma = true;
		}
		pr_cont("\n");
	}

	list_for_each_entry(work, &pool->worklist, entry) {
		if (get_work_pwq(work) == pwq) {
			has_pending = true;
			break;
		}
	}
	if (has_pending) {
		bool comma = false;

		pr_info("    pending:");
		list_for_each_entry(work, &pool->worklist, entry) {
			if (get_work_pwq(work) != pwq)
				continue;

			pr_cont_work(comma, work, &pcws);
			comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
		}
		pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
		pr_cont("\n");
	}

	if (!list_empty(&pwq->inactive_works)) {
		bool comma = false;

		pr_info("    inactive:");
		list_for_each_entry(work, &pwq->inactive_works, entry) {
			pr_cont_work(comma, work, &pcws);
			comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
		}
		pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
		pr_cont("\n");
	}
}

/**
 * show_one_workqueue - dump state of specified workqueue
 * @wq: workqueue whose state will be printed
 */
void show_one_workqueue(struct workqueue_struct *wq)
{
	struct pool_workqueue *pwq;
	bool idle = true;
	unsigned long irq_flags;

	for_each_pwq(pwq, wq) {
		if (!pwq_is_empty(pwq)) {
			idle = false;
			break;
		}
	}
	if (idle) /* Nothing to print for idle workqueue */
		return;

	pr_info("workqueue %s: flags=0x%x\n", wq->name, wq->flags);

	for_each_pwq(pwq, wq) {
		raw_spin_lock_irqsave(&pwq->pool->lock, irq_flags);
		if (!pwq_is_empty(pwq)) {
			/*
			 * Defer printing to avoid deadlocks in console
			 * drivers that queue work while holding locks
			 * also taken in their write paths.
			 */
			printk_deferred_enter();
			show_pwq(pwq);
			printk_deferred_exit();
		}
		raw_spin_unlock_irqrestore(&pwq->pool->lock, irq_flags);
		/*
		 * We could be printing a lot from atomic context, e.g.
		 * sysrq-t -> show_all_workqueues(). Avoid triggering
		 * hard lockup.
		 */
		touch_nmi_watchdog();
	}

}

/**
 * show_one_worker_pool - dump state of specified worker pool
 * @pool: worker pool whose state will be printed
 */
static void show_one_worker_pool(struct worker_pool *pool)
{
	struct worker *worker;
	bool first = true;
	unsigned long irq_flags;
	unsigned long hung = 0;

	raw_spin_lock_irqsave(&pool->lock, irq_flags);
	if (pool->nr_workers == pool->nr_idle)
		goto next_pool;

	/* How long the first pending work is waiting for a worker. */
	if (!list_empty(&pool->worklist))
		hung = jiffies_to_msecs(jiffies - pool->last_progress_ts) / 1000;

	/*
	 * Defer printing to avoid deadlocks in console drivers that
	 * queue work while holding locks also taken in their write
	 * paths.
	 */
	printk_deferred_enter();
	pr_info("pool %d:", pool->id);
	pr_cont_pool_info(pool);
	pr_cont(" hung=%lus workers=%d", hung, pool->nr_workers);
	if (pool->manager)
		pr_cont(" manager: %d",
			task_pid_nr(pool->manager->task));
	list_for_each_entry(worker, &pool->idle_list, entry) {
		pr_cont(" %s", first ? "idle: " : "");
		pr_cont_worker_id(worker);
		first = false;
	}
	pr_cont("\n");
	printk_deferred_exit();
next_pool:
	raw_spin_unlock_irqrestore(&pool->lock, irq_flags);
	/*
	 * We could be printing a lot from atomic context, e.g.
	 * sysrq-t -> show_all_workqueues(). Avoid triggering
	 * hard lockup.
	 */
	touch_nmi_watchdog();

}

/**
 * show_all_workqueues - dump workqueue state
 *
 * Called from a sysrq handler and prints out all busy workqueues and pools.
 */
void show_all_workqueues(void)
{
	struct workqueue_struct *wq;
	struct worker_pool *pool;
	int pi;

	rcu_read_lock();

	pr_info("Showing busy workqueues and worker pools:\n");

	list_for_each_entry_rcu(wq, &workqueues, list)
		show_one_workqueue(wq);

	for_each_pool(pool, pi)
		show_one_worker_pool(pool);

	rcu_read_unlock();
}

/**
 * show_freezable_workqueues - dump freezable workqueue state
 *
 * Called from try_to_freeze_tasks() and prints out all freezable workqueues
 * still busy.
 */
void show_freezable_workqueues(void)
{
	struct workqueue_struct *wq;

	rcu_read_lock();

	pr_info("Showing freezable workqueues that are still busy:\n");

	list_for_each_entry_rcu(wq, &workqueues, list) {
		if (!(wq->flags & WQ_FREEZABLE))
			continue;
		show_one_workqueue(wq);
	}

	rcu_read_unlock();
}

/* used to show worker information through /proc/PID/{comm,stat,status} */
void wq_worker_comm(char *buf, size_t size, struct task_struct *task)
{
	/* stabilize PF_WQ_WORKER and worker pool association */
	mutex_lock(&wq_pool_attach_mutex);

	if (task->flags & PF_WQ_WORKER) {
		struct worker *worker = kthread_data(task);
		struct worker_pool *pool = worker->pool;
		int off;

		off = format_worker_id(buf, size, worker, pool);

		if (pool) {
			raw_spin_lock_irq(&pool->lock);
			/*
			 * ->desc tracks information (wq name or
			 * set_worker_desc()) for the latest execution.  If
			 * current, prepend '+', otherwise '-'.
			 */
			if (worker->desc[0] != '\0') {
				if (worker->current_work)
					scnprintf(buf + off, size - off, "+%s",
						  worker->desc);
				else
					scnprintf(buf + off, size - off, "-%s",
						  worker->desc);
			}
			raw_spin_unlock_irq(&pool->lock);
		}
	} else {
		strscpy(buf, task->comm, size);
	}

	mutex_unlock(&wq_pool_attach_mutex);
}

#ifdef CONFIG_SMP

/*
 * CPU hotplug.
 *
 * There are two challenges in supporting CPU hotplug.  Firstly, there
 * are a lot of assumptions on strong associations among work, pwq and
 * pool which make migrating pending and scheduled works very
 * difficult to implement without impacting hot paths.  Secondly,
 * worker pools serve mix of short, long and very long running works making
 * blocked draining impractical.
 *
 * This is solved by allowing the pools to be disassociated from the CPU
 * running as an unbound one and allowing it to be reattached later if the
 * cpu comes back online.
 */

static void unbind_workers(int cpu)
{
	struct worker_pool *pool;
	struct worker *worker;

	for_each_cpu_worker_pool(pool, cpu) {
		mutex_lock(&wq_pool_attach_mutex);
		raw_spin_lock_irq(&pool->lock);

		/*
		 * We've blocked all attach/detach operations. Make all workers
		 * unbound and set DISASSOCIATED.  Before this, all workers
		 * must be on the cpu.  After this, they may become diasporas.
		 * And the preemption disabled section in their sched callbacks
		 * are guaranteed to see WORKER_UNBOUND since the code here
		 * is on the same cpu.
		 */
		for_each_pool_worker(worker, pool)
			worker->flags |= WORKER_UNBOUND;

		pool->flags |= POOL_DISASSOCIATED;

		/*
		 * The handling of nr_running in sched callbacks are disabled
		 * now.  Zap nr_running.  After this, nr_running stays zero and
		 * need_more_worker() and keep_working() are always true as
		 * long as the worklist is not empty.  This pool now behaves as
		 * an unbound (in terms of concurrency management) pool which
		 * are served by workers tied to the pool.
		 */
		pool->nr_running = 0;

		/*
		 * With concurrency management just turned off, a busy
		 * worker blocking could lead to lengthy stalls.  Kick off
		 * unbound chain execution of currently pending work items.
		 */
		kick_pool(pool);

		raw_spin_unlock_irq(&pool->lock);

		for_each_pool_worker(worker, pool)
			unbind_worker(worker);

		mutex_unlock(&wq_pool_attach_mutex);
	}
}

/**
 * rebind_workers - rebind all workers of a pool to the associated CPU
 * @pool: pool of interest
 *
 * @pool->cpu is coming online.  Rebind all workers to the CPU.
 */
static void rebind_workers(struct worker_pool *pool)
{
	struct worker *worker;

	lockdep_assert_held(&wq_pool_attach_mutex);

	/*
	 * Restore CPU affinity of all workers.  As all idle workers should
	 * be on the run-queue of the associated CPU before any local
	 * wake-ups for concurrency management happen, restore CPU affinity
	 * of all workers first and then clear UNBOUND.  As we're called
	 * from CPU_ONLINE, the following shouldn't fail.
	 */
	for_each_pool_worker(worker, pool) {
		kthread_set_per_cpu(worker->task, pool->cpu);
		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
						  pool_allowed_cpus(pool)) < 0);
	}

	raw_spin_lock_irq(&pool->lock);

	pool->flags &= ~POOL_DISASSOCIATED;

	for_each_pool_worker(worker, pool) {
		unsigned int worker_flags = worker->flags;

		/*
		 * We want to clear UNBOUND but can't directly call
		 * worker_clr_flags() or adjust nr_running.  Atomically
		 * replace UNBOUND with another NOT_RUNNING flag REBOUND.
		 * @worker will clear REBOUND using worker_clr_flags() when
		 * it initiates the next execution cycle thus restoring
		 * concurrency management.  Note that when or whether
		 * @worker clears REBOUND doesn't affect correctness.
		 *
		 * WRITE_ONCE() is necessary because @worker->flags may be
		 * tested without holding any lock in
		 * wq_worker_running().  Without it, NOT_RUNNING test may
		 * fail incorrectly leading to premature concurrency
		 * management operations.
		 */
		WARN_ON_ONCE(!(worker_flags & WORKER_UNBOUND));
		worker_flags |= WORKER_REBOUND;
		worker_flags &= ~WORKER_UNBOUND;
		WRITE_ONCE(worker->flags, worker_flags);
	}

	raw_spin_unlock_irq(&pool->lock);
}

/**
 * restore_unbound_workers_cpumask - restore cpumask of unbound workers
 * @pool: unbound pool of interest
 * @cpu: the CPU which is coming up
 *
 * An unbound pool may end up with a cpumask which doesn't have any online
 * CPUs.  When a worker of such pool get scheduled, the scheduler resets
 * its cpus_allowed.  If @cpu is in @pool's cpumask which didn't have any
 * online CPU before, cpus_allowed of all its workers should be restored.
 */
static void restore_unbound_workers_cpumask(struct worker_pool *pool, int cpu)
{
	static cpumask_t cpumask;
	struct worker *worker;

	lockdep_assert_held(&wq_pool_attach_mutex);

	/* is @cpu allowed for @pool? */
	if (!cpumask_test_cpu(cpu, pool->attrs->cpumask))
		return;

	cpumask_and(&cpumask, pool->attrs->cpumask, cpu_online_mask);

	/* as we're called from CPU_ONLINE, the following shouldn't fail */
	for_each_pool_worker(worker, pool)
		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, &cpumask) < 0);
}

int workqueue_prepare_cpu(unsigned int cpu)
{
	struct worker_pool *pool;

	for_each_cpu_worker_pool(pool, cpu) {
		if (pool->nr_workers)
			continue;
		if (!create_worker(pool))
			return -ENOMEM;
	}
	return 0;
}

int workqueue_online_cpu(unsigned int cpu)
{
	struct worker_pool *pool;
	struct workqueue_struct *wq;
	int pi;

	mutex_lock(&wq_pool_mutex);

	cpumask_set_cpu(cpu, wq_online_cpumask);

	for_each_pool(pool, pi) {
		/* BH pools aren't affected by hotplug */
		if (pool->flags & POOL_BH)
			continue;

		mutex_lock(&wq_pool_attach_mutex);
		if (pool->cpu == cpu)
			rebind_workers(pool);
		else if (pool->cpu < 0)
			restore_unbound_workers_cpumask(pool, cpu);
		mutex_unlock(&wq_pool_attach_mutex);
	}

	/* update pod affinity of unbound workqueues */
	list_for_each_entry(wq, &workqueues, list) {
		struct workqueue_attrs *attrs = wq->unbound_attrs;

		if (attrs) {
			const struct wq_pod_type *pt = wqattrs_pod_type(attrs);
			int tcpu;

			for_each_cpu(tcpu, pt->pod_cpus[pt->cpu_pod[cpu]])
				unbound_wq_update_pwq(wq, tcpu);

			mutex_lock(&wq->mutex);
			wq_update_node_max_active(wq, -1);
			mutex_unlock(&wq->mutex);
		}
	}

	mutex_unlock(&wq_pool_mutex);
	return 0;
}

int workqueue_offline_cpu(unsigned int cpu)
{
	struct workqueue_struct *wq;

	/* unbinding per-cpu workers should happen on the local CPU */
	if (WARN_ON(cpu != smp_processor_id()))
		return -1;

	unbind_workers(cpu);

	/* update pod affinity of unbound workqueues */
	mutex_lock(&wq_pool_mutex);

	cpumask_clear_cpu(cpu, wq_online_cpumask);

	list_for_each_entry(wq, &workqueues, list) {
		struct workqueue_attrs *attrs = wq->unbound_attrs;

		if (attrs) {
			const struct wq_pod_type *pt = wqattrs_pod_type(attrs);
			int tcpu;

			for_each_cpu(tcpu, pt->pod_cpus[pt->cpu_pod[cpu]])
				unbound_wq_update_pwq(wq, tcpu);

			mutex_lock(&wq->mutex);
			wq_update_node_max_active(wq, cpu);
			mutex_unlock(&wq->mutex);
		}
	}
	mutex_unlock(&wq_pool_mutex);

	return 0;
}

struct work_for_cpu {
	struct work_struct work;
	long (*fn)(void *);
	void *arg;
	long ret;
};

static void work_for_cpu_fn(struct work_struct *work)
{
	struct work_for_cpu *wfc = container_of(work, struct work_for_cpu, work);

	wfc->ret = wfc->fn(wfc->arg);
}

/**
 * work_on_cpu_key - run a function in thread context on a particular cpu
 * @cpu: the cpu to run on
 * @fn: the function to run
 * @arg: the function arg
 * @key: The lock class key for lock debugging purposes
 *
 * It is up to the caller to ensure that the cpu doesn't go offline.
 * The caller must not hold any locks which would prevent @fn from completing.
 *
 * Return: The value @fn returns.
 */
long work_on_cpu_key(int cpu, long (*fn)(void *),
		     void *arg, struct lock_class_key *key)
{
	struct work_for_cpu wfc = { .fn = fn, .arg = arg };

	INIT_WORK_ONSTACK_KEY(&wfc.work, work_for_cpu_fn, key);
	schedule_work_on(cpu, &wfc.work);
	flush_work(&wfc.work);
	destroy_work_on_stack(&wfc.work);
	return wfc.ret;
}
EXPORT_SYMBOL_GPL(work_on_cpu_key);
#endif /* CONFIG_SMP */

#ifdef CONFIG_FREEZER

/**
 * freeze_workqueues_begin - begin freezing workqueues
 *
 * Start freezing workqueues.  After this function returns, all freezable
 * workqueues will queue new works to their inactive_works list instead of
 * pool->worklist.
 *
 * CONTEXT:
 * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
 */
void freeze_workqueues_begin(void)
{
	struct workqueue_struct *wq;

	mutex_lock(&wq_pool_mutex);

	WARN_ON_ONCE(workqueue_freezing);
	workqueue_freezing = true;

	list_for_each_entry(wq, &workqueues, list) {
		mutex_lock(&wq->mutex);
		wq_adjust_max_active(wq);
		mutex_unlock(&wq->mutex);
	}

	mutex_unlock(&wq_pool_mutex);
}

/**
 * freeze_workqueues_busy - are freezable workqueues still busy?
 *
 * Check whether freezing is complete.  This function must be called
 * between freeze_workqueues_begin() and thaw_workqueues().
 *
 * CONTEXT:
 * Grabs and releases wq_pool_mutex.
 *
 * Return:
 * %true if some freezable workqueues are still busy.  %false if freezing
 * is complete.
 */
bool freeze_workqueues_busy(void)
{
	bool busy = false;
	struct workqueue_struct *wq;
	struct pool_workqueue *pwq;

	mutex_lock(&wq_pool_mutex);

	WARN_ON_ONCE(!workqueue_freezing);

	list_for_each_entry(wq, &workqueues, list) {
		if (!(wq->flags & WQ_FREEZABLE))
			continue;
		/*
		 * nr_active is monotonically decreasing.  It's safe
		 * to peek without lock.
		 */
		rcu_read_lock();
		for_each_pwq(pwq, wq) {
			WARN_ON_ONCE(pwq->nr_active < 0);
			if (pwq->nr_active) {
				busy = true;
				rcu_read_unlock();
				goto out_unlock;
			}
		}
		rcu_read_unlock();
	}
out_unlock:
	mutex_unlock(&wq_pool_mutex);
	return busy;
}

/**
 * thaw_workqueues - thaw workqueues
 *
 * Thaw workqueues.  Normal queueing is restored and all collected
 * frozen works are transferred to their respective pool worklists.
 *
 * CONTEXT:
 * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
 */
void thaw_workqueues(void)
{
	struct workqueue_struct *wq;

	mutex_lock(&wq_pool_mutex);

	if (!workqueue_freezing)
		goto out_unlock;

	workqueue_freezing = false;

	/* restore max_active and repopulate worklist */
	list_for_each_entry(wq, &workqueues, list) {
		mutex_lock(&wq->mutex);
		wq_adjust_max_active(wq);
		mutex_unlock(&wq->mutex);
	}

out_unlock:
	mutex_unlock(&wq_pool_mutex);
}
#endif /* CONFIG_FREEZER */

static int workqueue_apply_unbound_cpumask(const cpumask_var_t unbound_cpumask)
{
	LIST_HEAD(ctxs);
	int ret = 0;
	struct workqueue_struct *wq;
	struct apply_wqattrs_ctx *ctx, *n;

	lockdep_assert_held(&wq_pool_mutex);

	list_for_each_entry(wq, &workqueues, list) {
		if (!(wq->flags & WQ_UNBOUND) || (wq->flags & __WQ_DESTROYING))
			continue;

		ctx = apply_wqattrs_prepare(wq, wq->unbound_attrs, unbound_cpumask);
		if (IS_ERR(ctx)) {
			ret = PTR_ERR(ctx);
			break;
		}

		list_add_tail(&ctx->list, &ctxs);
	}

	list_for_each_entry_safe(ctx, n, &ctxs, list) {
		if (!ret)
			apply_wqattrs_commit(ctx);
		apply_wqattrs_cleanup(ctx);
	}

	if (!ret) {
		int cpu;
		struct worker_pool *pool;
		struct worker *worker;

		mutex_lock(&wq_pool_attach_mutex);
		cpumask_copy(wq_unbound_cpumask, unbound_cpumask);
		/* rescuer needs to respect cpumask changes when it is not attached */
		list_for_each_entry(wq, &workqueues, list) {
			if (wq->rescuer && !wq->rescuer->pool)
				unbind_worker(wq->rescuer);
		}
		/* DISASSOCIATED worker needs to respect wq_unbound_cpumask */
		for_each_possible_cpu(cpu) {
			for_each_cpu_worker_pool(pool, cpu) {
				if (!(pool->flags & POOL_DISASSOCIATED))
					continue;
				for_each_pool_worker(worker, pool)
					unbind_worker(worker);
			}
		}
		mutex_unlock(&wq_pool_attach_mutex);
	}
	return ret;
}

/**
 * workqueue_unbound_housekeeping_update - Propagate housekeeping cpumask update
 * @hk: the new housekeeping cpumask
 *
 * Update the unbound workqueue cpumask on top of the new housekeeping cpumask such
 * that the effective unbound affinity is the intersection of the new housekeeping
 * with the requested affinity set via nohz_full=/isolcpus= or sysfs.
 *
 * Return: 0 on success and -errno on failure.
 */
int workqueue_unbound_housekeeping_update(const struct cpumask *hk)
{
	cpumask_var_t cpumask;
	int ret = 0;

	if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
		return -ENOMEM;

	mutex_lock(&wq_pool_mutex);

	/*
	 * If the operation fails, it will fall back to
	 * wq_requested_unbound_cpumask which is initially set to
	 * HK_TYPE_DOMAIN house keeping mask and rewritten
	 * by any subsequent write to workqueue/cpumask sysfs file.
	 */
	if (!cpumask_and(cpumask, wq_requested_unbound_cpumask, hk))
		cpumask_copy(cpumask, wq_requested_unbound_cpumask);
	if (!cpumask_equal(cpumask, wq_unbound_cpumask))
		ret = workqueue_apply_unbound_cpumask(cpumask);

	/* Save the current isolated cpumask & export it via sysfs */
	if (!ret)
		cpumask_andnot(wq_isolated_cpumask, cpu_possible_mask, hk);

	mutex_unlock(&wq_pool_mutex);
	free_cpumask_var(cpumask);
	return ret;
}

static int parse_affn_scope(const char *val)
{
	return sysfs_match_string(wq_affn_names, val);
}

static int wq_affn_dfl_set(const char *val, const struct kernel_param *kp)
{
	struct workqueue_struct *wq;
	int affn, cpu;

	affn = parse_affn_scope(val);
	if (affn < 0)
		return affn;
	if (affn == WQ_AFFN_DFL)
		return -EINVAL;

	cpus_read_lock();
	mutex_lock(&wq_pool_mutex);

	wq_affn_dfl = affn;

	list_for_each_entry(wq, &workqueues, list) {
		for_each_online_cpu(cpu)
			unbound_wq_update_pwq(wq, cpu);
	}

	mutex_unlock(&wq_pool_mutex);
	cpus_read_unlock();

	return 0;
}

static int wq_affn_dfl_get(char *buffer, const struct kernel_param *kp)
{
	return scnprintf(buffer, PAGE_SIZE, "%s\n", wq_affn_names[wq_affn_dfl]);
}

static const struct kernel_param_ops wq_affn_dfl_ops = {
	.set	= wq_affn_dfl_set,
	.get	= wq_affn_dfl_get,
};

module_param_cb(default_affinity_scope, &wq_affn_dfl_ops, NULL, 0644);

#ifdef CONFIG_SYSFS
/*
 * Workqueues with WQ_SYSFS flag set is visible to userland via
 * /sys/bus/workqueue/devices/WQ_NAME.  All visible workqueues have the
 * following attributes.
 *
 *  per_cpu		RO bool	: whether the workqueue is per-cpu or unbound
 *  max_active		RW int	: maximum number of in-flight work items
 *
 * Unbound workqueues have the following extra attributes.
 *
 *  nice		RW int	: nice value of the workers
 *  cpumask		RW mask	: bitmask of allowed CPUs for the workers
 *  affinity_scope	RW str  : worker CPU affinity scope (cache, numa, none)
 *  affinity_strict	RW bool : worker CPU affinity is strict
 */
struct wq_device {
	struct workqueue_struct		*wq;
	struct device			dev;
};

static struct workqueue_struct *dev_to_wq(struct device *dev)
{
	struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);

	return wq_dev->wq;
}

static ssize_t per_cpu_show(struct device *dev, struct device_attribute *attr,
			    char *buf)
{
	struct workqueue_struct *wq = dev_to_wq(dev);

	return scnprintf(buf, PAGE_SIZE, "%d\n", (bool)!(wq->flags & WQ_UNBOUND));
}
static DEVICE_ATTR_RO(per_cpu);

static ssize_t max_active_show(struct device *dev,
			       struct device_attribute *attr, char *buf)
{
	struct workqueue_struct *wq = dev_to_wq(dev);

	return scnprintf(buf, PAGE_SIZE, "%d\n", wq->saved_max_active);
}

static ssize_t max_active_store(struct device *dev,
				struct device_attribute *attr, const char *buf,
				size_t count)
{
	struct workqueue_struct *wq = dev_to_wq(dev);
	int val;

	if (sscanf(buf, "%d", &val) != 1 || val <= 0)
		return -EINVAL;

	workqueue_set_max_active(wq, val);
	return count;
}
static DEVICE_ATTR_RW(max_active);

static struct attribute *wq_sysfs_attrs[] = {
	&dev_attr_per_cpu.attr,
	&dev_attr_max_active.attr,
	NULL,
};

static umode_t wq_sysfs_is_visible(struct kobject *kobj, struct attribute *a, int n)
{
	struct device *dev = kobj_to_dev(kobj);
	struct workqueue_struct *wq = dev_to_wq(dev);

	/*
	 * Adjusting max_active breaks ordering guarantee. Changing it has no
	 * effect on BH worker. Limit max_active to RO in such case.
	 */
	if (wq->flags & (WQ_BH | __WQ_ORDERED))
		return 0444;
	return a->mode;
}

static const struct attribute_group wq_sysfs_group = {
	.is_visible = wq_sysfs_is_visible,
	.attrs = wq_sysfs_attrs,
};
__ATTRIBUTE_GROUPS(wq_sysfs);

static ssize_t wq_nice_show(struct device *dev, struct device_attribute *attr,
			    char *buf)
{
	struct workqueue_struct *wq = dev_to_wq(dev);
	int written;

	mutex_lock(&wq->mutex);
	written = scnprintf(buf, PAGE_SIZE, "%d\n", wq->unbound_attrs->nice);
	mutex_unlock(&wq->mutex);

	return written;
}

/* prepare workqueue_attrs for sysfs store operations */
static struct workqueue_attrs *wq_sysfs_prep_attrs(struct workqueue_struct *wq)
{
	struct workqueue_attrs *attrs;

	lockdep_assert_held(&wq_pool_mutex);

	attrs = alloc_workqueue_attrs();
	if (!attrs)
		return NULL;

	copy_workqueue_attrs(attrs, wq->unbound_attrs);
	return attrs;
}

static ssize_t wq_nice_store(struct device *dev, struct device_attribute *attr,
			     const char *buf, size_t count)
{
	struct workqueue_struct *wq = dev_to_wq(dev);
	struct workqueue_attrs *attrs;
	int ret = -ENOMEM;

	apply_wqattrs_lock();

	attrs = wq_sysfs_prep_attrs(wq);
	if (!attrs)
		goto out_unlock;

	if (sscanf(buf, "%d", &attrs->nice) == 1 &&
	    attrs->nice >= MIN_NICE && attrs->nice <= MAX_NICE)
		ret = apply_workqueue_attrs_locked(wq, attrs);
	else
		ret = -EINVAL;

out_unlock:
	apply_wqattrs_unlock();
	free_workqueue_attrs(attrs);
	return ret ?: count;
}

static ssize_t wq_cpumask_show(struct device *dev,
			       struct device_attribute *attr, char *buf)
{
	struct workqueue_struct *wq = dev_to_wq(dev);
	int written;

	mutex_lock(&wq->mutex);
	written = scnprintf(buf, PAGE_SIZE, "%*pb\n",
			    cpumask_pr_args(wq->unbound_attrs->cpumask));
	mutex_unlock(&wq->mutex);
	return written;
}

static ssize_t wq_cpumask_store(struct device *dev,
				struct device_attribute *attr,
				const char *buf, size_t count)
{
	struct workqueue_struct *wq = dev_to_wq(dev);
	struct workqueue_attrs *attrs;
	int ret = -ENOMEM;

	apply_wqattrs_lock();

	attrs = wq_sysfs_prep_attrs(wq);
	if (!attrs)
		goto out_unlock;

	ret = cpumask_parse(buf, attrs->cpumask);
	if (!ret)
		ret = apply_workqueue_attrs_locked(wq, attrs);

out_unlock:
	apply_wqattrs_unlock();
	free_workqueue_attrs(attrs);
	return ret ?: count;
}

static ssize_t wq_affn_scope_show(struct device *dev,
				  struct device_attribute *attr, char *buf)
{
	struct workqueue_struct *wq = dev_to_wq(dev);
	int written;

	mutex_lock(&wq->mutex);
	if (wq->unbound_attrs->affn_scope == WQ_AFFN_DFL)
		written = scnprintf(buf, PAGE_SIZE, "%s (%s)\n",
				    wq_affn_names[WQ_AFFN_DFL],
				    wq_affn_names[wq_affn_dfl]);
	else
		written = scnprintf(buf, PAGE_SIZE, "%s\n",
				    wq_affn_names[wq->unbound_attrs->affn_scope]);
	mutex_unlock(&wq->mutex);

	return written;
}

static ssize_t wq_affn_scope_store(struct device *dev,
				   struct device_attribute *attr,
				   const char *buf, size_t count)
{
	struct workqueue_struct *wq = dev_to_wq(dev);
	struct workqueue_attrs *attrs;
	int affn, ret = -ENOMEM;

	affn = parse_affn_scope(buf);
	if (affn < 0)
		return affn;

	apply_wqattrs_lock();
	attrs = wq_sysfs_prep_attrs(wq);
	if (attrs) {
		attrs->affn_scope = affn;
		ret = apply_workqueue_attrs_locked(wq, attrs);
	}
	apply_wqattrs_unlock();
	free_workqueue_attrs(attrs);
	return ret ?: count;
}

static ssize_t wq_affinity_strict_show(struct device *dev,
				       struct device_attribute *attr, char *buf)
{
	struct workqueue_struct *wq = dev_to_wq(dev);

	return scnprintf(buf, PAGE_SIZE, "%d\n",
			 wq->unbound_attrs->affn_strict);
}

static ssize_t wq_affinity_strict_store(struct device *dev,
					struct device_attribute *attr,
					const char *buf, size_t count)
{
	struct workqueue_struct *wq = dev_to_wq(dev);
	struct workqueue_attrs *attrs;
	int v, ret = -ENOMEM;

	if (sscanf(buf, "%d", &v) != 1)
		return -EINVAL;

	apply_wqattrs_lock();
	attrs = wq_sysfs_prep_attrs(wq);
	if (attrs) {
		attrs->affn_strict = (bool)v;
		ret = apply_workqueue_attrs_locked(wq, attrs);
	}
	apply_wqattrs_unlock();
	free_workqueue_attrs(attrs);
	return ret ?: count;
}

static struct device_attribute wq_sysfs_unbound_attrs[] = {
	__ATTR(nice, 0644, wq_nice_show, wq_nice_store),
	__ATTR(cpumask, 0644, wq_cpumask_show, wq_cpumask_store),
	__ATTR(affinity_scope, 0644, wq_affn_scope_show, wq_affn_scope_store),
	__ATTR(affinity_strict, 0644, wq_affinity_strict_show, wq_affinity_strict_store),
	__ATTR_NULL,
};

static const struct bus_type wq_subsys = {
	.name				= "workqueue",
	.dev_groups			= wq_sysfs_groups,
};

/**
 *  workqueue_set_unbound_cpumask - Set the low-level unbound cpumask
 *  @cpumask: the cpumask to set
 *
 *  The low-level workqueues cpumask is a global cpumask that limits
 *  the affinity of all unbound workqueues.  This function check the @cpumask
 *  and apply it to all unbound workqueues and updates all pwqs of them.
 *
 *  Return:	0	- Success
 *		-EINVAL	- Invalid @cpumask
 *		-ENOMEM	- Failed to allocate memory for attrs or pwqs.
 */
static int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
{
	int ret = -EINVAL;

	/*
	 * Not excluding isolated cpus on purpose.
	 * If the user wishes to include them, we allow that.
	 */
	cpumask_and(cpumask, cpumask, cpu_possible_mask);
	if (!cpumask_empty(cpumask)) {
		ret = 0;
		apply_wqattrs_lock();
		if (!cpumask_equal(cpumask, wq_unbound_cpumask))
			ret = workqueue_apply_unbound_cpumask(cpumask);
		if (!ret)
			cpumask_copy(wq_requested_unbound_cpumask, cpumask);
		apply_wqattrs_unlock();
	}

	return ret;
}

static ssize_t __wq_cpumask_show(struct device *dev,
		struct device_attribute *attr, char *buf, cpumask_var_t mask)
{
	int written;

	mutex_lock(&wq_pool_mutex);
	written = scnprintf(buf, PAGE_SIZE, "%*pb\n", cpumask_pr_args(mask));
	mutex_unlock(&wq_pool_mutex);

	return written;
}

static ssize_t cpumask_requested_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	return __wq_cpumask_show(dev, attr, buf, wq_requested_unbound_cpumask);
}
static DEVICE_ATTR_RO(cpumask_requested);

static ssize_t cpumask_isolated_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	return __wq_cpumask_show(dev, attr, buf, wq_isolated_cpumask);
}
static DEVICE_ATTR_RO(cpumask_isolated);

static ssize_t cpumask_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	return __wq_cpumask_show(dev, attr, buf, wq_unbound_cpumask);
}

static ssize_t cpumask_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t count)
{
	cpumask_var_t cpumask;
	int ret;

	if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
		return -ENOMEM;

	ret = cpumask_parse(buf, cpumask);
	if (!ret)
		ret = workqueue_set_unbound_cpumask(cpumask);

	free_cpumask_var(cpumask);
	return ret ? ret : count;
}
static DEVICE_ATTR_RW(cpumask);

static struct attribute *wq_sysfs_cpumask_attrs[] = {
	&dev_attr_cpumask.attr,
	&dev_attr_cpumask_requested.attr,
	&dev_attr_cpumask_isolated.attr,
	NULL,
};
ATTRIBUTE_GROUPS(wq_sysfs_cpumask);

static int __init wq_sysfs_init(void)
{
	return subsys_virtual_register(&wq_subsys, wq_sysfs_cpumask_groups);
}
core_initcall(wq_sysfs_init);

static void wq_device_release(struct device *dev)
{
	struct wq_device *wq_dev = container_of(dev, struct wq_device, dev);

	kfree(wq_dev);
}

/**
 * workqueue_sysfs_register - make a workqueue visible in sysfs
 * @wq: the workqueue to register
 *
 * Expose @wq in sysfs under /sys/bus/workqueue/devices.
 * alloc_workqueue*() automatically calls this function if WQ_SYSFS is set
 * which is the preferred method.
 *
 * Workqueue user should use this function directly iff it wants to apply
 * workqueue_attrs before making the workqueue visible in sysfs; otherwise,
 * apply_workqueue_attrs() may race against userland updating the
 * attributes.
 *
 * Return: 0 on success, -errno on failure.
 */
int workqueue_sysfs_register(struct workqueue_struct *wq)
{
	struct wq_device *wq_dev;
	int ret;

	wq->wq_dev = wq_dev = kzalloc_obj(*wq_dev);
	if (!wq_dev)
		return -ENOMEM;

	wq_dev->wq = wq;
	wq_dev->dev.bus = &wq_subsys;
	wq_dev->dev.release = wq_device_release;
	dev_set_name(&wq_dev->dev, "%s", wq->name);

	/*
	 * unbound_attrs are created separately.  Suppress uevent until
	 * everything is ready.
	 */
	dev_set_uevent_suppress(&wq_dev->dev, true);

	ret = device_register(&wq_dev->dev);
	if (ret) {
		put_device(&wq_dev->dev);
		wq->wq_dev = NULL;
		return ret;
	}

	if (wq->flags & WQ_UNBOUND) {
		struct device_attribute *attr;

		for (attr = wq_sysfs_unbound_attrs; attr->attr.name; attr++) {
			ret = device_create_file(&wq_dev->dev, attr);
			if (ret) {
				device_unregister(&wq_dev->dev);
				wq->wq_dev = NULL;
				return ret;
			}
		}
	}

	dev_set_uevent_suppress(&wq_dev->dev, false);
	kobject_uevent(&wq_dev->dev.kobj, KOBJ_ADD);
	return 0;
}

/**
 * workqueue_sysfs_unregister - undo workqueue_sysfs_register()
 * @wq: the workqueue to unregister
 *
 * If @wq is registered to sysfs by workqueue_sysfs_register(), unregister.
 */
static void workqueue_sysfs_unregister(struct workqueue_struct *wq)
{
	struct wq_device *wq_dev = wq->wq_dev;

	if (!wq->wq_dev)
		return;

	wq->wq_dev = NULL;
	device_unregister(&wq_dev->dev);
}
#else	/* CONFIG_SYSFS */
static void workqueue_sysfs_unregister(struct workqueue_struct *wq)	{ }
#endif	/* CONFIG_SYSFS */

/*
 * Workqueue watchdog.
 *
 * Stall may be caused by various bugs - missing WQ_MEM_RECLAIM, illegal
 * flush dependency, a concurrency managed work item which stays RUNNING
 * indefinitely.  Workqueue stalls can be very difficult to debug as the
 * usual warning mechanisms don't trigger and internal workqueue state is
 * largely opaque.
 *
 * Workqueue watchdog monitors all worker pools periodically and dumps
 * state if some pools failed to make forward progress for a while where
 * forward progress is defined as the first item on ->worklist changing.
 *
 * This mechanism is controlled through the kernel parameter
 * "workqueue.watchdog_thresh" which can be updated at runtime through the
 * corresponding sysfs parameter file.
 */
#ifdef CONFIG_WQ_WATCHDOG

static unsigned long wq_watchdog_thresh = 30;
static struct timer_list wq_watchdog_timer;

static unsigned long wq_watchdog_touched = INITIAL_JIFFIES;
static DEFINE_PER_CPU(unsigned long, wq_watchdog_touched_cpu) = INITIAL_JIFFIES;

static unsigned int wq_panic_on_stall = CONFIG_BOOTPARAM_WQ_STALL_PANIC;
module_param_named(panic_on_stall, wq_panic_on_stall, uint, 0644);

static unsigned int wq_panic_on_stall_time;
module_param_named(panic_on_stall_time, wq_panic_on_stall_time, uint, 0644);
MODULE_PARM_DESC(panic_on_stall_time, "Panic if stall exceeds this many seconds (0=disabled)");

/*
 * Show workers that might prevent the processing of pending work items.
 * A busy worker that is not running on the CPU (e.g. sleeping in
 * wait_event_idle() with PF_WQ_WORKER cleared) can stall the pool just as
 * effectively as a CPU-bound one, so dump every in-flight worker.
 */
static void show_cpu_pool_busy_workers(struct worker_pool *pool)
{
	struct worker *worker;
	unsigned long irq_flags;
	int bkt;

	raw_spin_lock_irqsave(&pool->lock, irq_flags);

	hash_for_each(pool->busy_hash, bkt, worker, hentry) {
		/*
		 * Defer printing to avoid deadlocks in console
		 * drivers that queue work while holding locks
		 * also taken in their write paths.
		 */
		printk_deferred_enter();

		pr_info("pool %d:\n", pool->id);
		sched_show_task(worker->task);

		printk_deferred_exit();
	}

	raw_spin_unlock_irqrestore(&pool->lock, irq_flags);
}

static void show_cpu_pools_busy_workers(void)
{
	struct worker_pool *pool;
	int pi;

	pr_info("Showing backtraces of busy workers in stalled worker pools:\n");

	rcu_read_lock();

	for_each_pool(pool, pi) {
		if (pool->cpu_stall)
			show_cpu_pool_busy_workers(pool);

	}

	rcu_read_unlock();
}

/*
 * It triggers a panic in two scenarios: when the total number of stalls
 * exceeds a threshold, and when a stall lasts longer than
 * wq_panic_on_stall_time
 */
static void panic_on_wq_watchdog(unsigned int stall_time_sec)
{
	static unsigned int wq_stall;

	if (wq_panic_on_stall) {
		wq_stall++;
		if (wq_stall >= wq_panic_on_stall)
			panic("workqueue: %u stall(s) exceeded threshold %u\n",
			      wq_stall, wq_panic_on_stall);
	}

	if (wq_panic_on_stall_time && stall_time_sec >= wq_panic_on_stall_time)
		panic("workqueue: stall lasted %us, exceeding threshold %us\n",
		      stall_time_sec, wq_panic_on_stall_time);
}

static void wq_watchdog_reset_touched(void)
{
	int cpu;

	wq_watchdog_touched = jiffies;
	for_each_possible_cpu(cpu)
		per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
}

static void wq_watchdog_timer_fn(struct timer_list *unused)
{
	unsigned long thresh = READ_ONCE(wq_watchdog_thresh) * HZ;
	unsigned int max_stall_time = 0;
	bool lockup_detected = false;
	bool cpu_pool_stall = false;
	unsigned long now = jiffies;
	struct worker_pool *pool;
	unsigned int stall_time;
	int pi;

	if (!thresh)
		return;

	for_each_pool(pool, pi) {
		unsigned long pool_ts, touched, ts;

		pool->cpu_stall = false;
		if (list_empty(&pool->worklist))
			continue;

		/*
		 * If a virtual machine is stopped by the host it can look to
		 * the watchdog like a stall.
		 */
		kvm_check_and_clear_guest_paused();

		/* get the latest of pool and touched timestamps */
		if (pool->cpu >= 0)
			touched = READ_ONCE(per_cpu(wq_watchdog_touched_cpu, pool->cpu));
		else
			touched = READ_ONCE(wq_watchdog_touched);
		pool_ts = READ_ONCE(pool->last_progress_ts);

		if (time_after(pool_ts, touched))
			ts = pool_ts;
		else
			ts = touched;

		/*
		 * Did we stall?
		 *
		 * Do a lockless check first to do not disturb the system.
		 *
		 * Prevent false positives by double checking the timestamp
		 * under pool->lock. The lock makes sure that the check reads
		 * an updated pool->last_progress_ts when this CPU saw
		 * an already updated pool->worklist above. It seems better
		 * than adding another barrier into __queue_work() which
		 * is a hotter path.
		 */
		if (time_after(now, ts + thresh)) {
			scoped_guard(raw_spinlock_irqsave, &pool->lock) {
				pool_ts = pool->last_progress_ts;
				if (time_after(pool_ts, touched))
					ts = pool_ts;
				else
					ts = touched;
			}
			if (!time_after(now, ts + thresh))
				continue;

			lockup_detected = true;
			stall_time = jiffies_to_msecs(now - pool_ts) / 1000;
			max_stall_time = max(max_stall_time, stall_time);
			if (pool->cpu >= 0 && !(pool->flags & POOL_BH)) {
				pool->cpu_stall = true;
				cpu_pool_stall = true;
			}
			pr_emerg("BUG: workqueue lockup - pool");
			pr_cont_pool_info(pool);
			pr_cont(" stuck for %us!\n", stall_time);
		}
	}

	if (lockup_detected)
		show_all_workqueues();

	if (cpu_pool_stall)
		show_cpu_pools_busy_workers();

	if (lockup_detected)
		panic_on_wq_watchdog(max_stall_time);

	wq_watchdog_reset_touched();
	mod_timer(&wq_watchdog_timer, jiffies + thresh);
}

notrace void wq_watchdog_touch(int cpu)
{
	unsigned long thresh = READ_ONCE(wq_watchdog_thresh) * HZ;
	unsigned long touch_ts = READ_ONCE(wq_watchdog_touched);
	unsigned long now = jiffies;

	if (cpu >= 0)
		per_cpu(wq_watchdog_touched_cpu, cpu) = now;
	else
		WARN_ONCE(1, "%s should be called with valid CPU", __func__);

	/* Don't unnecessarily store to global cacheline */
	if (time_after(now, touch_ts + thresh / 4))
		WRITE_ONCE(wq_watchdog_touched, jiffies);
}

static void wq_watchdog_set_thresh(unsigned long thresh)
{
	wq_watchdog_thresh = 0;
	timer_delete_sync(&wq_watchdog_timer);

	if (thresh) {
		wq_watchdog_thresh = thresh;
		wq_watchdog_reset_touched();
		mod_timer(&wq_watchdog_timer, jiffies + thresh * HZ);
	}
}

static int wq_watchdog_param_set_thresh(const char *val,
					const struct kernel_param *kp)
{
	unsigned long thresh;
	int ret;

	ret = kstrtoul(val, 0, &thresh);
	if (ret)
		return ret;

	if (system_percpu_wq)
		wq_watchdog_set_thresh(thresh);
	else
		wq_watchdog_thresh = thresh;

	return 0;
}

static const struct kernel_param_ops wq_watchdog_thresh_ops = {
	.set	= wq_watchdog_param_set_thresh,
	.get	= param_get_ulong,
};

module_param_cb(watchdog_thresh, &wq_watchdog_thresh_ops, &wq_watchdog_thresh,
		0644);

static void wq_watchdog_init(void)
{
	timer_setup(&wq_watchdog_timer, wq_watchdog_timer_fn, TIMER_DEFERRABLE);
	wq_watchdog_set_thresh(wq_watchdog_thresh);
}

#else	/* CONFIG_WQ_WATCHDOG */

static inline void wq_watchdog_init(void) { }

#endif	/* CONFIG_WQ_WATCHDOG */

static void bh_pool_kick_normal(struct irq_work *irq_work)
{
	raise_softirq_irqoff(TASKLET_SOFTIRQ);
}

static void bh_pool_kick_highpri(struct irq_work *irq_work)
{
	raise_softirq_irqoff(HI_SOFTIRQ);
}

static void __init restrict_unbound_cpumask(const char *name, const struct cpumask *mask)
{
	if (!cpumask_intersects(wq_unbound_cpumask, mask)) {
		pr_warn("workqueue: Restricting unbound_cpumask (%*pb) with %s (%*pb) leaves no CPU, ignoring\n",
			cpumask_pr_args(wq_unbound_cpumask), name, cpumask_pr_args(mask));
		return;
	}

	cpumask_and(wq_unbound_cpumask, wq_unbound_cpumask, mask);
}

static void __init init_cpu_worker_pool(struct worker_pool *pool, int cpu, int nice)
{
	BUG_ON(init_worker_pool(pool));
	pool->cpu = cpu;
	cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
	cpumask_copy(pool->attrs->__pod_cpumask, cpumask_of(cpu));
	pool->attrs->nice = nice;
	pool->attrs->affn_strict = true;
	pool->node = cpu_to_node(cpu);

	/* alloc pool ID */
	mutex_lock(&wq_pool_mutex);
	BUG_ON(worker_pool_assign_id(pool));
	mutex_unlock(&wq_pool_mutex);
}

/**
 * workqueue_init_early - early init for workqueue subsystem
 *
 * This is the first step of three-staged workqueue subsystem initialization and
 * invoked as soon as the bare basics - memory allocation, cpumasks and idr are
 * up. It sets up all the data structures and system workqueues and allows early
 * boot code to create workqueues and queue/cancel work items. Actual work item
 * execution starts only after kthreads can be created and scheduled right
 * before early initcalls.
 */
void __init workqueue_init_early(void)
{
	struct wq_pod_type *pt = &wq_pod_types[WQ_AFFN_SYSTEM];
	int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL };
	void (*irq_work_fns[NR_STD_WORKER_POOLS])(struct irq_work *) =
		{ bh_pool_kick_normal, bh_pool_kick_highpri };
	int i, cpu;

	BUILD_BUG_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));

	BUG_ON(!alloc_cpumask_var(&wq_online_cpumask, GFP_KERNEL));
	BUG_ON(!alloc_cpumask_var(&wq_unbound_cpumask, GFP_KERNEL));
	BUG_ON(!alloc_cpumask_var(&wq_requested_unbound_cpumask, GFP_KERNEL));
	BUG_ON(!zalloc_cpumask_var(&wq_isolated_cpumask, GFP_KERNEL));

	cpumask_copy(wq_online_cpumask, cpu_online_mask);
	cpumask_copy(wq_unbound_cpumask, cpu_possible_mask);
	restrict_unbound_cpumask("HK_TYPE_DOMAIN", housekeeping_cpumask(HK_TYPE_DOMAIN));
	if (!cpumask_empty(&wq_cmdline_cpumask))
		restrict_unbound_cpumask("workqueue.unbound_cpus", &wq_cmdline_cpumask);

	cpumask_copy(wq_requested_unbound_cpumask, wq_unbound_cpumask);
	cpumask_andnot(wq_isolated_cpumask, cpu_possible_mask,
						housekeeping_cpumask(HK_TYPE_DOMAIN));
	pwq_cache = KMEM_CACHE(pool_workqueue, SLAB_PANIC);

	unbound_wq_update_pwq_attrs_buf = alloc_workqueue_attrs();
	BUG_ON(!unbound_wq_update_pwq_attrs_buf);

	/*
	 * If nohz_full is enabled, set power efficient workqueue as unbound.
	 * This allows workqueue items to be moved to HK CPUs.
	 */
	if (housekeeping_enabled(HK_TYPE_TICK))
		wq_power_efficient = true;

	/* initialize WQ_AFFN_SYSTEM pods */
	pt->pod_cpus = kzalloc_objs(pt->pod_cpus[0], 1);
	pt->pod_node = kzalloc_objs(pt->pod_node[0], 1);
	pt->cpu_pod = kzalloc_objs(pt->cpu_pod[0], nr_cpu_ids);
	BUG_ON(!pt->pod_cpus || !pt->pod_node || !pt->cpu_pod);

	BUG_ON(!zalloc_cpumask_var_node(&pt->pod_cpus[0], GFP_KERNEL, NUMA_NO_NODE));

	pt->nr_pods = 1;
	cpumask_copy(pt->pod_cpus[0], cpu_possible_mask);
	pt->pod_node[0] = NUMA_NO_NODE;
	pt->cpu_pod[0] = 0;

	/* initialize BH and CPU pools */
	for_each_possible_cpu(cpu) {
		struct worker_pool *pool;

		i = 0;
		for_each_bh_worker_pool(pool, cpu) {
			init_cpu_worker_pool(pool, cpu, std_nice[i]);
			pool->flags |= POOL_BH;
			init_irq_work(bh_pool_irq_work(pool), irq_work_fns[i]);
			i++;
		}

		i = 0;
		for_each_cpu_worker_pool(pool, cpu)
			init_cpu_worker_pool(pool, cpu, std_nice[i++]);
	}

	/* create default unbound and ordered wq attrs */
	for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
		struct workqueue_attrs *attrs;

		BUG_ON(!(attrs = alloc_workqueue_attrs()));
		attrs->nice = std_nice[i];
		unbound_std_wq_attrs[i] = attrs;

		/*
		 * An ordered wq should have only one pwq as ordering is
		 * guaranteed by max_active which is enforced by pwqs.
		 */
		BUG_ON(!(attrs = alloc_workqueue_attrs()));
		attrs->nice = std_nice[i];
		attrs->ordered = true;
		ordered_wq_attrs[i] = attrs;
	}

	system_wq = alloc_workqueue("events", WQ_PERCPU, 0);
	system_percpu_wq = alloc_workqueue("events", WQ_PERCPU, 0);
	system_highpri_wq = alloc_workqueue("events_highpri",
					    WQ_HIGHPRI | WQ_PERCPU, 0);
	system_long_wq = alloc_workqueue("events_long", WQ_PERCPU, 0);
	system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND, WQ_MAX_ACTIVE);
	system_dfl_wq = alloc_workqueue("events_unbound", WQ_UNBOUND, WQ_MAX_ACTIVE);
	system_freezable_wq = alloc_workqueue("events_freezable",
					      WQ_FREEZABLE | WQ_PERCPU, 0);
	system_power_efficient_wq = alloc_workqueue("events_power_efficient",
					      WQ_POWER_EFFICIENT | WQ_PERCPU, 0);
	system_freezable_power_efficient_wq = alloc_workqueue("events_freezable_pwr_efficient",
					      WQ_FREEZABLE | WQ_POWER_EFFICIENT | WQ_PERCPU, 0);
	system_bh_wq = alloc_workqueue("events_bh", WQ_BH | WQ_PERCPU, 0);
	system_bh_highpri_wq = alloc_workqueue("events_bh_highpri",
					       WQ_BH | WQ_HIGHPRI | WQ_PERCPU, 0);
	system_dfl_long_wq = alloc_workqueue("events_dfl_long", WQ_UNBOUND, WQ_MAX_ACTIVE);
	BUG_ON(!system_wq || !system_percpu_wq|| !system_highpri_wq || !system_long_wq ||
	       !system_unbound_wq || !system_freezable_wq || !system_dfl_wq ||
	       !system_power_efficient_wq ||
	       !system_freezable_power_efficient_wq ||
	       !system_bh_wq || !system_bh_highpri_wq || !system_dfl_long_wq);
}

static void __init wq_cpu_intensive_thresh_init(void)
{
	unsigned long thresh;
	unsigned long bogo;

	pwq_release_worker = kthread_run_worker(0, "pool_workqueue_release");
	BUG_ON(IS_ERR(pwq_release_worker));

	/* if the user set it to a specific value, keep it */
	if (wq_cpu_intensive_thresh_us != ULONG_MAX)
		return;

	/*
	 * The default of 10ms is derived from the fact that most modern (as of
	 * 2023) processors can do a lot in 10ms and that it's just below what
	 * most consider human-perceivable. However, the kernel also runs on a
	 * lot slower CPUs including microcontrollers where the threshold is way
	 * too low.
	 *
	 * Let's scale up the threshold upto 1 second if BogoMips is below 4000.
	 * This is by no means accurate but it doesn't have to be. The mechanism
	 * is still useful even when the threshold is fully scaled up. Also, as
	 * the reports would usually be applicable to everyone, some machines
	 * operating on longer thresholds won't significantly diminish their
	 * usefulness.
	 */
	thresh = 10 * USEC_PER_MSEC;

	/* see init/calibrate.c for lpj -> BogoMIPS calculation */
	bogo = max_t(unsigned long, loops_per_jiffy / 500000 * HZ, 1);
	if (bogo < 4000)
		thresh = min_t(unsigned long, thresh * 4000 / bogo, USEC_PER_SEC);

	pr_debug("wq_cpu_intensive_thresh: lpj=%lu BogoMIPS=%lu thresh_us=%lu\n",
		 loops_per_jiffy, bogo, thresh);

	wq_cpu_intensive_thresh_us = thresh;
}

/**
 * workqueue_init - bring workqueue subsystem fully online
 *
 * This is the second step of three-staged workqueue subsystem initialization
 * and invoked as soon as kthreads can be created and scheduled. Workqueues have
 * been created and work items queued on them, but there are no kworkers
 * executing the work items yet. Populate the worker pools with the initial
 * workers and enable future kworker creations.
 */
void __init workqueue_init(void)
{
	struct workqueue_struct *wq;
	struct worker_pool *pool;
	int cpu, bkt;

	wq_cpu_intensive_thresh_init();

	mutex_lock(&wq_pool_mutex);

	/*
	 * Per-cpu pools created earlier could be missing node hint. Fix them
	 * up. Also, create a rescuer for workqueues that requested it.
	 */
	for_each_possible_cpu(cpu) {
		for_each_bh_worker_pool(pool, cpu)
			pool->node = cpu_to_node(cpu);
		for_each_cpu_worker_pool(pool, cpu)
			pool->node = cpu_to_node(cpu);
	}

	list_for_each_entry(wq, &workqueues, list) {
		WARN(init_rescuer(wq),
		     "workqueue: failed to create early rescuer for %s",
		     wq->name);
	}

	mutex_unlock(&wq_pool_mutex);

	/*
	 * Create the initial workers. A BH pool has one pseudo worker that
	 * represents the shared BH execution context and thus doesn't get
	 * affected by hotplug events. Create the BH pseudo workers for all
	 * possible CPUs here.
	 */
	for_each_possible_cpu(cpu)
		for_each_bh_worker_pool(pool, cpu)
			BUG_ON(!create_worker(pool));

	for_each_online_cpu(cpu) {
		for_each_cpu_worker_pool(pool, cpu) {
			pool->flags &= ~POOL_DISASSOCIATED;
			BUG_ON(!create_worker(pool));
		}
	}

	hash_for_each(unbound_pool_hash, bkt, pool, hash_node)
		BUG_ON(!create_worker(pool));

	wq_online = true;
	wq_watchdog_init();
}

/*
 * Initialize @pt by first initializing @pt->cpu_pod[] with pod IDs according to
 * @cpu_shares_pod(). Each subset of CPUs that share a pod is assigned a unique
 * and consecutive pod ID. The rest of @pt is initialized accordingly.
 */
static void __init init_pod_type(struct wq_pod_type *pt,
				 bool (*cpus_share_pod)(int, int))
{
	int cur, pre, cpu, pod;

	pt->nr_pods = 0;

	/* init @pt->cpu_pod[] according to @cpus_share_pod() */
	pt->cpu_pod = kzalloc_objs(pt->cpu_pod[0], nr_cpu_ids);
	BUG_ON(!pt->cpu_pod);

	for_each_possible_cpu(cur) {
		for_each_possible_cpu(pre) {
			if (pre >= cur) {
				pt->cpu_pod[cur] = pt->nr_pods++;
				break;
			}
			if (cpus_share_pod(cur, pre)) {
				pt->cpu_pod[cur] = pt->cpu_pod[pre];
				break;
			}
		}
	}

	/* init the rest to match @pt->cpu_pod[] */
	pt->pod_cpus = kzalloc_objs(pt->pod_cpus[0], pt->nr_pods);
	pt->pod_node = kzalloc_objs(pt->pod_node[0], pt->nr_pods);
	BUG_ON(!pt->pod_cpus || !pt->pod_node);

	for (pod = 0; pod < pt->nr_pods; pod++)
		BUG_ON(!zalloc_cpumask_var(&pt->pod_cpus[pod], GFP_KERNEL));

	for_each_possible_cpu(cpu) {
		cpumask_set_cpu(cpu, pt->pod_cpus[pt->cpu_pod[cpu]]);
		pt->pod_node[pt->cpu_pod[cpu]] = cpu_to_node(cpu);
	}
}

static bool __init cpus_dont_share(int cpu0, int cpu1)
{
	return false;
}

static bool __init cpus_share_smt(int cpu0, int cpu1)
{
#ifdef CONFIG_SCHED_SMT
	return cpumask_test_cpu(cpu0, cpu_smt_mask(cpu1));
#else
	return false;
#endif
}

static bool __init cpus_share_numa(int cpu0, int cpu1)
{
	return cpu_to_node(cpu0) == cpu_to_node(cpu1);
}

/* Maps each CPU to its shard index within the LLC pod it belongs to */
static int cpu_shard_id[NR_CPUS] __initdata;

/**
 * llc_count_cores - count distinct cores (SMT groups) within an LLC pod
 * @pod_cpus:  the cpumask of CPUs in the LLC pod
 * @smt_pods:  the SMT pod type, used to identify sibling groups
 *
 * A core is represented by the lowest-numbered CPU in its SMT group. Returns
 * the number of distinct cores found in @pod_cpus.
 */
static int __init llc_count_cores(const struct cpumask *pod_cpus,
				  struct wq_pod_type *smt_pods)
{
	const struct cpumask *sibling_cpus;
	int nr_cores = 0, c;

	/*
	 * Count distinct cores by only counting the first CPU in each
	 * SMT sibling group.
	 */
	for_each_cpu(c, pod_cpus) {
		sibling_cpus = smt_pods->pod_cpus[smt_pods->cpu_pod[c]];
		if (cpumask_first(sibling_cpus) == c)
			nr_cores++;
	}

	return nr_cores;
}

/*
 * llc_shard_size - number of cores in a given shard
 *
 * Cores are spread as evenly as possible. The first @nr_large_shards shards are
 * "large shards" with (cores_per_shard + 1) cores; the rest are "default
 * shards" with cores_per_shard cores.
 */
static int __init llc_shard_size(int shard_id, int cores_per_shard, int nr_large_shards)
{
	/* The first @nr_large_shards shards are large shards */
	if (shard_id < nr_large_shards)
		return cores_per_shard + 1;

	/* The remaining shards are default shards */
	return cores_per_shard;
}

/*
 * llc_calc_shard_layout - compute the shard layout for an LLC pod
 * @nr_cores:  number of distinct cores in the LLC pod
 *
 * Chooses the number of shards that keeps average shard size closest to
 * wq_cache_shard_size. Returns a struct describing the total number of shards,
 * the base size of each, and how many are large shards.
 */
static struct llc_shard_layout __init llc_calc_shard_layout(int nr_cores)
{
	struct llc_shard_layout layout;

	/* Ensure at least one shard; pick the count closest to the target size */
	layout.nr_shards = max(1, DIV_ROUND_CLOSEST(nr_cores, wq_cache_shard_size));
	layout.cores_per_shard = nr_cores / layout.nr_shards;
	layout.nr_large_shards = nr_cores % layout.nr_shards;

	return layout;
}

/*
 * llc_shard_is_full - check whether a shard has reached its core capacity
 * @cores_in_shard: number of cores already assigned to this shard
 * @shard_id:       index of the shard being checked
 * @layout:         the shard layout computed by llc_calc_shard_layout()
 *
 * Returns true if @cores_in_shard equals the expected size for @shard_id.
 */
static bool __init llc_shard_is_full(int cores_in_shard, int shard_id,
				     const struct llc_shard_layout *layout)
{
	return cores_in_shard == llc_shard_size(shard_id, layout->cores_per_shard,
						layout->nr_large_shards);
}

/**
 * llc_populate_cpu_shard_id - populate cpu_shard_id[] for each CPU in an LLC pod
 * @pod_cpus:  the cpumask of CPUs in the LLC pod
 * @smt_pods:  the SMT pod type, used to identify sibling groups
 * @nr_cores:  number of distinct cores in @pod_cpus (from llc_count_cores())
 *
 * Walks @pod_cpus in order. At each SMT group leader, advances to the next
 * shard once the current shard is full. Results are written to cpu_shard_id[].
 */
static void __init llc_populate_cpu_shard_id(const struct cpumask *pod_cpus,
					     struct wq_pod_type *smt_pods,
					     int nr_cores)
{
	struct llc_shard_layout layout = llc_calc_shard_layout(nr_cores);
	const struct cpumask *sibling_cpus;
	/* Count the number of cores in the current shard_id */
	int cores_in_shard = 0;
	unsigned int leader;
	/* This is a cursor for the shards. Go from zero to nr_shards - 1*/
	int shard_id = 0;
	int c;

	/* Iterate at every CPU for a given LLC pod, and assign it a shard */
	for_each_cpu(c, pod_cpus) {
		sibling_cpus = smt_pods->pod_cpus[smt_pods->cpu_pod[c]];
		if (cpumask_first(sibling_cpus) == c) {
			/* This is the CPU leader for the siblings */
			if (llc_shard_is_full(cores_in_shard, shard_id, &layout)) {
				shard_id++;
				cores_in_shard = 0;
			}
			cores_in_shard++;
			cpu_shard_id[c] = shard_id;
		} else {
			/*
			 * The siblings' shard MUST be the same as the leader.
			 * never split threads in the same core.
			 */
			leader = cpumask_first(sibling_cpus);

			/*
			 * This check silences a Warray-bounds warning on UP
			 * configs where NR_CPUS=1 makes cpu_shard_id[]
			 * a single-element array, and the compiler can't
			 * prove the index is always 0.
			 */
			if (WARN_ON_ONCE(leader >= nr_cpu_ids))
				continue;
			cpu_shard_id[c] = cpu_shard_id[leader];
		}
	}

	WARN_ON_ONCE(shard_id != (layout.nr_shards - 1));
}

/**
 * precompute_cache_shard_ids - assign each CPU its shard index within its LLC
 *
 * Iterates over all LLC pods. For each pod, counts distinct cores then assigns
 * shard indices to all CPUs in the pod. Must be called after WQ_AFFN_CACHE and
 * WQ_AFFN_SMT have been initialized.
 */
static void __init precompute_cache_shard_ids(void)
{
	struct wq_pod_type *llc_pods = &wq_pod_types[WQ_AFFN_CACHE];
	struct wq_pod_type *smt_pods = &wq_pod_types[WQ_AFFN_SMT];
	const struct cpumask *cpus_sharing_llc;
	int nr_cores;
	int pod;

	if (!wq_cache_shard_size) {
		pr_warn("workqueue: cache_shard_size must be > 0, setting to 1\n");
		wq_cache_shard_size = 1;
	}

	for (pod = 0; pod < llc_pods->nr_pods; pod++) {
		cpus_sharing_llc = llc_pods->pod_cpus[pod];

		/* Number of cores in this given LLC */
		nr_cores = llc_count_cores(cpus_sharing_llc, smt_pods);
		llc_populate_cpu_shard_id(cpus_sharing_llc, smt_pods, nr_cores);
	}
}

/*
 * cpus_share_cache_shard - test whether two CPUs belong to the same cache shard
 *
 * Two CPUs share a cache shard if they are in the same LLC and have the same
 * shard index. Used as the pod affinity callback for WQ_AFFN_CACHE_SHARD.
 */
static bool __init cpus_share_cache_shard(int cpu0, int cpu1)
{
	if (!cpus_share_cache(cpu0, cpu1))
		return false;

	return cpu_shard_id[cpu0] == cpu_shard_id[cpu1];
}

/**
 * workqueue_init_topology - initialize CPU pods for unbound workqueues
 *
 * This is the third step of three-staged workqueue subsystem initialization and
 * invoked after SMP and topology information are fully initialized. It
 * initializes the unbound CPU pods accordingly.
 */
void __init workqueue_init_topology(void)
{
	struct workqueue_struct *wq;
	int cpu;

	init_pod_type(&wq_pod_types[WQ_AFFN_CPU], cpus_dont_share);
	init_pod_type(&wq_pod_types[WQ_AFFN_SMT], cpus_share_smt);
	init_pod_type(&wq_pod_types[WQ_AFFN_CACHE], cpus_share_cache);
	precompute_cache_shard_ids();
	init_pod_type(&wq_pod_types[WQ_AFFN_CACHE_SHARD], cpus_share_cache_shard);
	init_pod_type(&wq_pod_types[WQ_AFFN_NUMA], cpus_share_numa);

	wq_topo_initialized = true;

	mutex_lock(&wq_pool_mutex);

	/*
	 * Workqueues allocated earlier would have all CPUs sharing the default
	 * worker pool. Explicitly call unbound_wq_update_pwq() on all workqueue
	 * and CPU combinations to apply per-pod sharing.
	 */
	list_for_each_entry(wq, &workqueues, list) {
		for_each_online_cpu(cpu)
			unbound_wq_update_pwq(wq, cpu);
		if (wq->flags & WQ_UNBOUND) {
			mutex_lock(&wq->mutex);
			wq_update_node_max_active(wq, -1);
			mutex_unlock(&wq->mutex);
		}
	}

	mutex_unlock(&wq_pool_mutex);
}

void __warn_flushing_systemwide_wq(void)
{
	pr_warn("WARNING: Flushing system-wide workqueues will be prohibited in near future.\n");
	dump_stack();
}
EXPORT_SYMBOL(__warn_flushing_systemwide_wq);

static int __init workqueue_unbound_cpus_setup(char *str)
{
	if (cpulist_parse(str, &wq_cmdline_cpumask) < 0) {
		cpumask_clear(&wq_cmdline_cpumask);
		pr_warn("workqueue.unbound_cpus: incorrect CPU range, using default\n");
	}

	return 1;
}
__setup("workqueue.unbound_cpus=", workqueue_unbound_cpus_setup);