xref: /linux/kernel/rcu/tree.h (revision ed7171ff9fabc49ae6ed42fbd082a576473836fc)
1 /* SPDX-License-Identifier: GPL-2.0+ */
2 /*
3  * Read-Copy Update mechanism for mutual exclusion (tree-based version)
4  * Internal non-public definitions.
5  *
6  * Copyright IBM Corporation, 2008
7  *
8  * Author: Ingo Molnar <mingo@elte.hu>
9  *	   Paul E. McKenney <paulmck@linux.ibm.com>
10  */
11 
12 #include <linux/cache.h>
13 #include <linux/kthread.h>
14 #include <linux/spinlock.h>
15 #include <linux/rtmutex.h>
16 #include <linux/threads.h>
17 #include <linux/cpumask.h>
18 #include <linux/seqlock.h>
19 #include <linux/swait.h>
20 #include <linux/rcu_node_tree.h>
21 
22 #include "rcu_segcblist.h"
23 
24 /* Communicate arguments to a kthread worker handler. */
25 struct rcu_exp_work {
26 	unsigned long rew_s;
27 	struct kthread_work rew_work;
28 };
29 
30 /* RCU's kthread states for tracing. */
31 #define RCU_KTHREAD_STOPPED  0
32 #define RCU_KTHREAD_RUNNING  1
33 #define RCU_KTHREAD_WAITING  2
34 #define RCU_KTHREAD_OFFCPU   3
35 #define RCU_KTHREAD_YIELDING 4
36 #define RCU_KTHREAD_MAX      4
37 
38 /*
39  * Definition for node within the RCU grace-period-detection hierarchy.
40  */
41 struct rcu_node {
42 	raw_spinlock_t __private lock;	/* Root rcu_node's lock protects */
43 					/*  some rcu_state fields as well as */
44 					/*  following. */
45 	unsigned long gp_seq;	/* Track rsp->gp_seq. */
46 	unsigned long gp_seq_needed; /* Track furthest future GP request. */
47 	unsigned long completedqs; /* All QSes done for this node. */
48 	unsigned long qsmask;	/* CPUs or groups that need to switch in */
49 				/*  order for current grace period to proceed.*/
50 				/*  In leaf rcu_node, each bit corresponds to */
51 				/*  an rcu_data structure, otherwise, each */
52 				/*  bit corresponds to a child rcu_node */
53 				/*  structure. */
54 	unsigned long rcu_gp_init_mask;	/* Mask of offline CPUs at GP init. */
55 	unsigned long qsmaskinit;
56 				/* Per-GP initial value for qsmask. */
57 				/*  Initialized from ->qsmaskinitnext at the */
58 				/*  beginning of each grace period. */
59 	unsigned long qsmaskinitnext;
60 	unsigned long expmask;	/* CPUs or groups that need to check in */
61 				/*  to allow the current expedited GP */
62 				/*  to complete. */
63 	unsigned long expmaskinit;
64 				/* Per-GP initial values for expmask. */
65 				/*  Initialized from ->expmaskinitnext at the */
66 				/*  beginning of each expedited GP. */
67 	unsigned long expmaskinitnext;
68 				/* Online CPUs for next expedited GP. */
69 				/*  Any CPU that has ever been online will */
70 				/*  have its bit set. */
71 	struct kthread_worker *exp_kworker;
72 				/* Workers performing per node expedited GP */
73 				/* initialization. */
74 	unsigned long cbovldmask;
75 				/* CPUs experiencing callback overload. */
76 	unsigned long ffmask;	/* Fully functional CPUs. */
77 	unsigned long grpmask;	/* Mask to apply to parent qsmask. */
78 				/*  Only one bit will be set in this mask. */
79 	int	grplo;		/* lowest-numbered CPU here. */
80 	int	grphi;		/* highest-numbered CPU here. */
81 	u8	grpnum;		/* group number for next level up. */
82 	u8	level;		/* root is at level 0. */
83 	bool	wait_blkd_tasks;/* Necessary to wait for blocked tasks to */
84 				/*  exit RCU read-side critical sections */
85 				/*  before propagating offline up the */
86 				/*  rcu_node tree? */
87 	struct rcu_node *parent;
88 	struct list_head blkd_tasks;
89 				/* Tasks blocked in RCU read-side critical */
90 				/*  section.  Tasks are placed at the head */
91 				/*  of this list and age towards the tail. */
92 	struct list_head *gp_tasks;
93 				/* Pointer to the first task blocking the */
94 				/*  current grace period, or NULL if there */
95 				/*  is no such task. */
96 	struct list_head *exp_tasks;
97 				/* Pointer to the first task blocking the */
98 				/*  current expedited grace period, or NULL */
99 				/*  if there is no such task.  If there */
100 				/*  is no current expedited grace period, */
101 				/*  then there can cannot be any such task. */
102 	struct list_head *boost_tasks;
103 				/* Pointer to first task that needs to be */
104 				/*  priority boosted, or NULL if no priority */
105 				/*  boosting is needed for this rcu_node */
106 				/*  structure.  If there are no tasks */
107 				/*  queued on this rcu_node structure that */
108 				/*  are blocking the current grace period, */
109 				/*  there can be no such task. */
110 	struct rt_mutex boost_mtx;
111 				/* Used only for the priority-boosting */
112 				/*  side effect, not as a lock. */
113 	unsigned long boost_time;
114 				/* When to start boosting (jiffies). */
115 	struct mutex kthread_mutex;
116 				/* Exclusion for thread spawning and affinity */
117 				/*  manipulation. */
118 	struct task_struct *boost_kthread_task;
119 				/* kthread that takes care of priority */
120 				/*  boosting for this rcu_node structure. */
121 	unsigned int boost_kthread_status;
122 				/* State of boost_kthread_task for tracing. */
123 	unsigned long n_boosts;	/* Number of boosts for this rcu_node structure. */
124 #ifdef CONFIG_RCU_NOCB_CPU
125 	struct swait_queue_head nocb_gp_wq[2];
126 				/* Place for rcu_nocb_kthread() to wait GP. */
127 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
128 	raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
129 
130 	spinlock_t exp_lock ____cacheline_internodealigned_in_smp;
131 	unsigned long exp_seq_rq;
132 	wait_queue_head_t exp_wq[4];
133 	struct rcu_exp_work rew;
134 	bool exp_need_flush;	/* Need to flush workitem? */
135 	raw_spinlock_t exp_poll_lock;
136 				/* Lock and data for polled expedited grace periods. */
137 	unsigned long exp_seq_poll_rq;
138 	struct work_struct exp_poll_wq;
139 } ____cacheline_internodealigned_in_smp;
140 
141 /*
142  * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and
143  * are indexed relative to this interval rather than the global CPU ID space.
144  * This generates the bit for a CPU in node-local masks.
145  */
146 #define leaf_node_cpu_bit(rnp, cpu) (BIT((cpu) - (rnp)->grplo))
147 
148 /*
149  * Union to allow "aggregate OR" operation on the need for a quiescent
150  * state by the normal and expedited grace periods.
151  */
152 union rcu_noqs {
153 	struct {
154 		u8 norm;
155 		u8 exp;
156 	} b; /* Bits. */
157 	u16 s; /* Set of bits, aggregate OR here. */
158 };
159 
160 /*
161  * Record the snapshot of the core stats at half of the first RCU stall timeout.
162  * The member gp_seq is used to ensure that all members are updated only once
163  * during the sampling period. The snapshot is taken only if this gp_seq is not
164  * equal to rdp->gp_seq.
165  */
166 struct rcu_snap_record {
167 	unsigned long	gp_seq;		/* Track rdp->gp_seq counter */
168 	u64		cputime_irq;	/* Accumulated cputime of hard irqs */
169 	u64		cputime_softirq;/* Accumulated cputime of soft irqs */
170 	u64		cputime_system; /* Accumulated cputime of kernel tasks */
171 	unsigned long	nr_hardirqs;	/* Accumulated number of hard irqs */
172 	unsigned int	nr_softirqs;	/* Accumulated number of soft irqs */
173 	unsigned long long nr_csw;	/* Accumulated number of task switches */
174 	unsigned long   jiffies;	/* Track jiffies value */
175 };
176 
177 /* Per-CPU data for read-copy update. */
178 struct rcu_data {
179 	/* 1) quiescent-state and grace-period handling : */
180 	unsigned long	gp_seq;		/* Track rsp->gp_seq counter. */
181 	unsigned long	gp_seq_needed;	/* Track furthest future GP request. */
182 	union rcu_noqs	cpu_no_qs;	/* No QSes yet for this CPU. */
183 	bool		core_needs_qs;	/* Core waits for quiescent state. */
184 	bool		beenonline;	/* CPU online at least once. */
185 	bool		gpwrap;		/* Possible ->gp_seq wrap. */
186 	bool		cpu_started;	/* RCU watching this onlining CPU. */
187 	struct rcu_node *mynode;	/* This CPU's leaf of hierarchy */
188 	unsigned long grpmask;		/* Mask to apply to leaf qsmask. */
189 	unsigned long	ticks_this_gp;	/* The number of scheduling-clock */
190 					/*  ticks this CPU has handled */
191 					/*  during and after the last grace */
192 					/* period it is aware of. */
193 	struct irq_work defer_qs_iw;	/* Obtain later scheduler attention. */
194 	bool defer_qs_iw_pending;	/* Scheduler attention pending? */
195 	struct work_struct strict_work;	/* Schedule readers for strict GPs. */
196 
197 	/* 2) batch handling */
198 	struct rcu_segcblist cblist;	/* Segmented callback list, with */
199 					/* different callbacks waiting for */
200 					/* different grace periods. */
201 	long		qlen_last_fqs_check;
202 					/* qlen at last check for QS forcing */
203 	unsigned long	n_cbs_invoked;	/* # callbacks invoked since boot. */
204 	unsigned long	n_force_qs_snap;
205 					/* did other CPU force QS recently? */
206 	long		blimit;		/* Upper limit on a processed batch */
207 
208 	/* 3) dynticks interface. */
209 	int dynticks_snap;		/* Per-GP tracking for dynticks. */
210 	bool rcu_need_heavy_qs;		/* GP old, so heavy quiescent state! */
211 	bool rcu_urgent_qs;		/* GP old need light quiescent state. */
212 	bool rcu_forced_tick;		/* Forced tick to provide QS. */
213 	bool rcu_forced_tick_exp;	/*   ... provide QS to expedited GP. */
214 
215 	/* 4) rcu_barrier(), OOM callbacks, and expediting. */
216 	unsigned long barrier_seq_snap;	/* Snap of rcu_state.barrier_sequence. */
217 	struct rcu_head barrier_head;
218 	int exp_dynticks_snap;		/* Double-check need for IPI. */
219 
220 	/* 5) Callback offloading. */
221 #ifdef CONFIG_RCU_NOCB_CPU
222 	struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */
223 	struct swait_queue_head nocb_state_wq; /* For offloading state changes */
224 	struct task_struct *nocb_gp_kthread;
225 	raw_spinlock_t nocb_lock;	/* Guard following pair of fields. */
226 	int nocb_defer_wakeup;		/* Defer wakeup of nocb_kthread. */
227 	struct timer_list nocb_timer;	/* Enforce finite deferral. */
228 	unsigned long nocb_gp_adv_time;	/* Last call_rcu() CB adv (jiffies). */
229 	struct mutex nocb_gp_kthread_mutex; /* Exclusion for nocb gp kthread */
230 					    /* spawning */
231 
232 	/* The following fields are used by call_rcu, hence own cacheline. */
233 	raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp;
234 	struct rcu_cblist nocb_bypass;	/* Lock-contention-bypass CB list. */
235 	unsigned long nocb_bypass_first; /* Time (jiffies) of first enqueue. */
236 	unsigned long nocb_nobypass_last; /* Last ->cblist enqueue (jiffies). */
237 	int nocb_nobypass_count;	/* # ->cblist enqueues at ^^^ time. */
238 
239 	/* The following fields are used by GP kthread, hence own cacheline. */
240 	raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp;
241 	u8 nocb_gp_sleep;		/* Is the nocb GP thread asleep? */
242 	u8 nocb_gp_bypass;		/* Found a bypass on last scan? */
243 	u8 nocb_gp_gp;			/* GP to wait for on last scan? */
244 	unsigned long nocb_gp_seq;	/*  If so, ->gp_seq to wait for. */
245 	unsigned long nocb_gp_loops;	/* # passes through wait code. */
246 	struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */
247 	bool nocb_cb_sleep;		/* Is the nocb CB thread asleep? */
248 	struct task_struct *nocb_cb_kthread;
249 	struct list_head nocb_head_rdp; /*
250 					 * Head of rcu_data list in wakeup chain,
251 					 * if rdp_gp.
252 					 */
253 	struct list_head nocb_entry_rdp; /* rcu_data node in wakeup chain. */
254 	struct rcu_data *nocb_toggling_rdp; /* rdp queued for (de-)offloading */
255 
256 	/* The following fields are used by CB kthread, hence new cacheline. */
257 	struct rcu_data *nocb_gp_rdp ____cacheline_internodealigned_in_smp;
258 					/* GP rdp takes GP-end wakeups. */
259 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
260 
261 	/* 6) RCU priority boosting. */
262 	struct task_struct *rcu_cpu_kthread_task;
263 					/* rcuc per-CPU kthread or NULL. */
264 	unsigned int rcu_cpu_kthread_status;
265 	char rcu_cpu_has_work;
266 	unsigned long rcuc_activity;
267 
268 	/* 7) Diagnostic data, including RCU CPU stall warnings. */
269 	unsigned int softirq_snap;	/* Snapshot of softirq activity. */
270 	/* ->rcu_iw* fields protected by leaf rcu_node ->lock. */
271 	struct irq_work rcu_iw;		/* Check for non-irq activity. */
272 	bool rcu_iw_pending;		/* Is ->rcu_iw pending? */
273 	unsigned long rcu_iw_gp_seq;	/* ->gp_seq associated with ->rcu_iw. */
274 	unsigned long rcu_ofl_gp_seq;	/* ->gp_seq at last offline. */
275 	short rcu_ofl_gp_state;		/* ->gp_state at last offline. */
276 	unsigned long rcu_onl_gp_seq;	/* ->gp_seq at last online. */
277 	short rcu_onl_gp_state;		/* ->gp_state at last online. */
278 	unsigned long last_fqs_resched;	/* Time of last rcu_resched(). */
279 	unsigned long last_sched_clock;	/* Jiffies of last rcu_sched_clock_irq(). */
280 	struct rcu_snap_record snap_record; /* Snapshot of core stats at half of */
281 					    /* the first RCU stall timeout */
282 
283 	long lazy_len;			/* Length of buffered lazy callbacks. */
284 	int cpu;
285 };
286 
287 /* Values for nocb_defer_wakeup field in struct rcu_data. */
288 #define RCU_NOCB_WAKE_NOT	0
289 #define RCU_NOCB_WAKE_BYPASS	1
290 #define RCU_NOCB_WAKE_LAZY	2
291 #define RCU_NOCB_WAKE		3
292 #define RCU_NOCB_WAKE_FORCE	4
293 
294 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
295 					/* For jiffies_till_first_fqs and */
296 					/*  and jiffies_till_next_fqs. */
297 
298 #define RCU_JIFFIES_FQS_DIV	256	/* Very large systems need more */
299 					/*  delay between bouts of */
300 					/*  quiescent-state forcing. */
301 
302 #define RCU_STALL_RAT_DELAY	2	/* Allow other CPUs time to take */
303 					/*  at least one scheduling clock */
304 					/*  irq before ratting on them. */
305 
306 #define rcu_wait(cond)							\
307 do {									\
308 	for (;;) {							\
309 		set_current_state(TASK_INTERRUPTIBLE);			\
310 		if (cond)						\
311 			break;						\
312 		schedule();						\
313 	}								\
314 	__set_current_state(TASK_RUNNING);				\
315 } while (0)
316 
317 /*
318  * A max threshold for synchronize_rcu() users which are
319  * awaken directly by the rcu_gp_kthread(). Left part is
320  * deferred to the main worker.
321  */
322 #define SR_MAX_USERS_WAKE_FROM_GP 5
323 #define SR_NORMAL_GP_WAIT_HEAD_MAX 5
324 
325 struct sr_wait_node {
326 	atomic_t inuse;
327 	struct llist_node node;
328 };
329 
330 /*
331  * RCU global state, including node hierarchy.  This hierarchy is
332  * represented in "heap" form in a dense array.  The root (first level)
333  * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
334  * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
335  * and the third level in ->node[m+1] and following (->node[m+1] referenced
336  * by ->level[2]).  The number of levels is determined by the number of
337  * CPUs and by CONFIG_RCU_FANOUT.  Small systems will have a "hierarchy"
338  * consisting of a single rcu_node.
339  */
340 struct rcu_state {
341 	struct rcu_node node[NUM_RCU_NODES];	/* Hierarchy. */
342 	struct rcu_node *level[RCU_NUM_LVLS + 1];
343 						/* Hierarchy levels (+1 to */
344 						/*  shut bogus gcc warning) */
345 	int ncpus;				/* # CPUs seen so far. */
346 	int n_online_cpus;			/* # CPUs online for RCU. */
347 
348 	/* The following fields are guarded by the root rcu_node's lock. */
349 
350 	unsigned long gp_seq ____cacheline_internodealigned_in_smp;
351 						/* Grace-period sequence #. */
352 	unsigned long gp_max;			/* Maximum GP duration in */
353 						/*  jiffies. */
354 	struct task_struct *gp_kthread;		/* Task for grace periods. */
355 	struct swait_queue_head gp_wq;		/* Where GP task waits. */
356 	short gp_flags;				/* Commands for GP task. */
357 	short gp_state;				/* GP kthread sleep state. */
358 	unsigned long gp_wake_time;		/* Last GP kthread wake. */
359 	unsigned long gp_wake_seq;		/* ->gp_seq at ^^^. */
360 	unsigned long gp_seq_polled;		/* GP seq for polled API. */
361 	unsigned long gp_seq_polled_snap;	/* ->gp_seq_polled at normal GP start. */
362 	unsigned long gp_seq_polled_exp_snap;	/* ->gp_seq_polled at expedited GP start. */
363 
364 	/* End of fields guarded by root rcu_node's lock. */
365 
366 	struct mutex barrier_mutex;		/* Guards barrier fields. */
367 	atomic_t barrier_cpu_count;		/* # CPUs waiting on. */
368 	struct completion barrier_completion;	/* Wake at barrier end. */
369 	unsigned long barrier_sequence;		/* ++ at start and end of */
370 						/*  rcu_barrier(). */
371 	/* End of fields guarded by barrier_mutex. */
372 
373 	raw_spinlock_t barrier_lock;		/* Protects ->barrier_seq_snap. */
374 
375 	struct mutex exp_mutex;			/* Serialize expedited GP. */
376 	struct mutex exp_wake_mutex;		/* Serialize wakeup. */
377 	unsigned long expedited_sequence;	/* Take a ticket. */
378 	atomic_t expedited_need_qs;		/* # CPUs left to check in. */
379 	struct swait_queue_head expedited_wq;	/* Wait for check-ins. */
380 	int ncpus_snap;				/* # CPUs seen last time. */
381 	u8 cbovld;				/* Callback overload now? */
382 	u8 cbovldnext;				/* ^        ^  next time? */
383 
384 	unsigned long jiffies_force_qs;		/* Time at which to invoke */
385 						/*  force_quiescent_state(). */
386 	unsigned long jiffies_kick_kthreads;	/* Time at which to kick */
387 						/*  kthreads, if configured. */
388 	unsigned long n_force_qs;		/* Number of calls to */
389 						/*  force_quiescent_state(). */
390 	unsigned long gp_start;			/* Time at which GP started, */
391 						/*  but in jiffies. */
392 	unsigned long gp_end;			/* Time last GP ended, again */
393 						/*  in jiffies. */
394 	unsigned long gp_activity;		/* Time of last GP kthread */
395 						/*  activity in jiffies. */
396 	unsigned long gp_req_activity;		/* Time of last GP request */
397 						/*  in jiffies. */
398 	unsigned long jiffies_stall;		/* Time at which to check */
399 						/*  for CPU stalls. */
400 	int nr_fqs_jiffies_stall;		/* Number of fqs loops after
401 						 * which read jiffies and set
402 						 * jiffies_stall. Stall
403 						 * warnings disabled if !0. */
404 	unsigned long jiffies_resched;		/* Time at which to resched */
405 						/*  a reluctant CPU. */
406 	unsigned long n_force_qs_gpstart;	/* Snapshot of n_force_qs at */
407 						/*  GP start. */
408 	const char *name;			/* Name of structure. */
409 	char abbr;				/* Abbreviated name. */
410 
411 	arch_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
412 						/* Synchronize offline with */
413 						/*  GP pre-initialization. */
414 	int nocb_is_setup;			/* nocb is setup from boot */
415 
416 	/* synchronize_rcu() part. */
417 	struct llist_head srs_next;	/* request a GP users. */
418 	struct llist_node *srs_wait_tail; /* wait for GP users. */
419 	struct llist_node *srs_done_tail; /* ready for GP users. */
420 	struct sr_wait_node srs_wait_nodes[SR_NORMAL_GP_WAIT_HEAD_MAX];
421 	struct work_struct srs_cleanup_work;
422 	atomic_t srs_cleanups_pending; /* srs inflight worker cleanups. */
423 };
424 
425 /* Values for rcu_state structure's gp_flags field. */
426 #define RCU_GP_FLAG_INIT 0x1	/* Need grace-period initialization. */
427 #define RCU_GP_FLAG_FQS  0x2	/* Need grace-period quiescent-state forcing. */
428 #define RCU_GP_FLAG_OVLD 0x4	/* Experiencing callback overload. */
429 
430 /* Values for rcu_state structure's gp_state field. */
431 #define RCU_GP_IDLE	 0	/* Initial state and no GP in progress. */
432 #define RCU_GP_WAIT_GPS  1	/* Wait for grace-period start. */
433 #define RCU_GP_DONE_GPS  2	/* Wait done for grace-period start. */
434 #define RCU_GP_ONOFF     3	/* Grace-period initialization hotplug. */
435 #define RCU_GP_INIT      4	/* Grace-period initialization. */
436 #define RCU_GP_WAIT_FQS  5	/* Wait for force-quiescent-state time. */
437 #define RCU_GP_DOING_FQS 6	/* Wait done for force-quiescent-state time. */
438 #define RCU_GP_CLEANUP   7	/* Grace-period cleanup started. */
439 #define RCU_GP_CLEANED   8	/* Grace-period cleanup complete. */
440 
441 /*
442  * In order to export the rcu_state name to the tracing tools, it
443  * needs to be added in the __tracepoint_string section.
444  * This requires defining a separate variable tp_<sname>_varname
445  * that points to the string being used, and this will allow
446  * the tracing userspace tools to be able to decipher the string
447  * address to the matching string.
448  */
449 #ifdef CONFIG_PREEMPT_RCU
450 #define RCU_ABBR 'p'
451 #define RCU_NAME_RAW "rcu_preempt"
452 #else /* #ifdef CONFIG_PREEMPT_RCU */
453 #define RCU_ABBR 's'
454 #define RCU_NAME_RAW "rcu_sched"
455 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
456 #ifndef CONFIG_TRACING
457 #define RCU_NAME RCU_NAME_RAW
458 #else /* #ifdef CONFIG_TRACING */
459 static char rcu_name[] = RCU_NAME_RAW;
460 static const char *tp_rcu_varname __used __tracepoint_string = rcu_name;
461 #define RCU_NAME rcu_name
462 #endif /* #else #ifdef CONFIG_TRACING */
463 
464 /* Forward declarations for tree_plugin.h */
465 static void rcu_bootup_announce(void);
466 static void rcu_qs(void);
467 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
468 #ifdef CONFIG_HOTPLUG_CPU
469 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
470 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
471 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
472 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
473 static void rcu_flavor_sched_clock_irq(int user);
474 static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
475 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
476 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
477 static bool rcu_is_callbacks_kthread(struct rcu_data *rdp);
478 static void rcu_cpu_kthread_setup(unsigned int cpu);
479 static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp);
480 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
481 static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
482 static void zero_cpu_stall_ticks(struct rcu_data *rdp);
483 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
484 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
485 static void rcu_init_one_nocb(struct rcu_node *rnp);
486 static bool wake_nocb_gp(struct rcu_data *rdp, bool force);
487 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
488 				  unsigned long j, bool lazy);
489 static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
490 			  rcu_callback_t func, unsigned long flags, bool lazy);
491 static void __maybe_unused __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
492 						unsigned long flags);
493 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level);
494 static bool do_nocb_deferred_wakeup(struct rcu_data *rdp);
495 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
496 static void rcu_spawn_cpu_nocb_kthread(int cpu);
497 static void show_rcu_nocb_state(struct rcu_data *rdp);
498 static void rcu_nocb_lock(struct rcu_data *rdp);
499 static void rcu_nocb_unlock(struct rcu_data *rdp);
500 static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
501 				       unsigned long flags);
502 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp);
503 #ifdef CONFIG_RCU_NOCB_CPU
504 static void __init rcu_organize_nocb_kthreads(void);
505 
506 /*
507  * Disable IRQs before checking offloaded state so that local
508  * locking is safe against concurrent de-offloading.
509  */
510 #define rcu_nocb_lock_irqsave(rdp, flags)			\
511 do {								\
512 	local_irq_save(flags);					\
513 	if (rcu_segcblist_is_offloaded(&(rdp)->cblist))	\
514 		raw_spin_lock(&(rdp)->nocb_lock);		\
515 } while (0)
516 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
517 #define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags)
518 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
519 
520 static void rcu_bind_gp_kthread(void);
521 static bool rcu_nohz_full_cpu(void);
522 
523 /* Forward declarations for tree_stall.h */
524 static void record_gp_stall_check_time(void);
525 static void rcu_iw_handler(struct irq_work *iwp);
526 static void check_cpu_stall(struct rcu_data *rdp);
527 static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
528 				     const unsigned long gpssdelay);
529 
530 /* Forward declarations for tree_exp.h. */
531 static void sync_rcu_do_polled_gp(struct work_struct *wp);
532