xref: /linux/kernel/bpf/bpf_local_storage.c (revision eb71ab2bf72260054677e348498ba995a057c463)

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019 Facebook  */
#include <linux/rculist.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/types.h>
#include <linux/spinlock.h>
#include <linux/bpf.h>
#include <linux/btf_ids.h>
#include <linux/bpf_local_storage.h>
#include <net/sock.h>
#include <uapi/linux/sock_diag.h>
#include <uapi/linux/btf.h>
#include <linux/rcupdate.h>
#include <linux/rcupdate_trace.h>
#include <linux/rcupdate_wait.h>

#define BPF_LOCAL_STORAGE_CREATE_FLAG_MASK (BPF_F_NO_PREALLOC | BPF_F_CLONE)

static struct bpf_local_storage_map_bucket *
select_bucket(struct bpf_local_storage_map *smap,
	      struct bpf_local_storage *local_storage)
{
	return &smap->buckets[hash_ptr(local_storage, smap->bucket_log)];
}

static int mem_charge(struct bpf_local_storage_map *smap, void *owner, u32 size)
{
	struct bpf_map *map = &smap->map;

	if (!map->ops->map_local_storage_charge)
		return 0;

	return map->ops->map_local_storage_charge(smap, owner, size);
}

static void mem_uncharge(struct bpf_local_storage_map *smap, void *owner,
			 u32 size)
{
	struct bpf_map *map = &smap->map;

	if (map->ops->map_local_storage_uncharge)
		map->ops->map_local_storage_uncharge(smap, owner, size);
}

static struct bpf_local_storage __rcu **
owner_storage(struct bpf_local_storage_map *smap, void *owner)
{
	struct bpf_map *map = &smap->map;

	return map->ops->map_owner_storage_ptr(owner);
}

static bool selem_linked_to_storage_lockless(const struct bpf_local_storage_elem *selem)
{
	return !hlist_unhashed_lockless(&selem->snode);
}

static bool selem_linked_to_storage(const struct bpf_local_storage_elem *selem)
{
	return !hlist_unhashed(&selem->snode);
}

static bool selem_linked_to_map(const struct bpf_local_storage_elem *selem)
{
	return !hlist_unhashed(&selem->map_node);
}

struct bpf_local_storage_elem *
bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
		void *value, bool swap_uptrs, gfp_t gfp_flags)
{
	struct bpf_local_storage_elem *selem;

	if (mem_charge(smap, owner, smap->elem_size))
		return NULL;

	if (smap->use_kmalloc_nolock) {
		selem = bpf_map_kmalloc_nolock(&smap->map, smap->elem_size,
					       __GFP_ZERO, NUMA_NO_NODE);
	} else {
		selem = bpf_map_kzalloc(&smap->map, smap->elem_size,
					gfp_flags | __GFP_NOWARN);
	}

	if (selem) {
		RCU_INIT_POINTER(SDATA(selem)->smap, smap);
		atomic_set(&selem->state, 0);
		selem->use_kmalloc_nolock = smap->use_kmalloc_nolock;

		if (value) {
			/* No need to call check_and_init_map_value as memory is zero init */
			copy_map_value(&smap->map, SDATA(selem)->data, value);
			if (swap_uptrs)
				bpf_obj_swap_uptrs(smap->map.record, SDATA(selem)->data, value);
		}
		return selem;
	}

	mem_uncharge(smap, owner, smap->elem_size);

	return NULL;
}

/* rcu tasks trace callback for use_kmalloc_nolock == false */
static void __bpf_local_storage_free_trace_rcu(struct rcu_head *rcu)
{
	struct bpf_local_storage *local_storage;

	/*
	 * RCU Tasks Trace grace period implies RCU grace period, do
	 * kfree() directly.
	 */
	local_storage = container_of(rcu, struct bpf_local_storage, rcu);
	kfree(local_storage);
}

/* Handle use_kmalloc_nolock == false */
static void __bpf_local_storage_free(struct bpf_local_storage *local_storage,
				     bool vanilla_rcu)
{
	if (vanilla_rcu)
		kfree_rcu(local_storage, rcu);
	else
		call_rcu_tasks_trace(&local_storage->rcu,
				     __bpf_local_storage_free_trace_rcu);
}

static void bpf_local_storage_free_rcu(struct rcu_head *rcu)
{
	struct bpf_local_storage *local_storage;

	local_storage = container_of(rcu, struct bpf_local_storage, rcu);
	kfree_nolock(local_storage);
}

static void bpf_local_storage_free_trace_rcu(struct rcu_head *rcu)
{
	/*
	 * RCU Tasks Trace grace period implies RCU grace period, do
	 * kfree() directly.
	 */
	bpf_local_storage_free_rcu(rcu);
}

static void bpf_local_storage_free(struct bpf_local_storage *local_storage,
				   bool reuse_now)
{
	if (!local_storage)
		return;

	if (!local_storage->use_kmalloc_nolock) {
		__bpf_local_storage_free(local_storage, reuse_now);
		return;
	}

	if (reuse_now) {
		call_rcu(&local_storage->rcu, bpf_local_storage_free_rcu);
		return;
	}

	call_rcu_tasks_trace(&local_storage->rcu,
			     bpf_local_storage_free_trace_rcu);
}

/* rcu callback for use_kmalloc_nolock == false */
static void __bpf_selem_free_rcu(struct rcu_head *rcu)
{
	struct bpf_local_storage_elem *selem;
	struct bpf_local_storage_map *smap;

	selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
	/* bpf_selem_unlink_nofail may have already cleared smap and freed fields. */
	smap = rcu_dereference_check(SDATA(selem)->smap, 1);

	if (smap)
		bpf_obj_free_fields(smap->map.record, SDATA(selem)->data);
	kfree(selem);
}

/* rcu tasks trace callback for use_kmalloc_nolock == false */
static void __bpf_selem_free_trace_rcu(struct rcu_head *rcu)
{
	/*
	 * RCU Tasks Trace grace period implies RCU grace period, do
	 * kfree() directly.
	 */
	__bpf_selem_free_rcu(rcu);
}

/* Handle use_kmalloc_nolock == false */
static void __bpf_selem_free(struct bpf_local_storage_elem *selem,
			     bool vanilla_rcu)
{
	if (vanilla_rcu)
		call_rcu(&selem->rcu, __bpf_selem_free_rcu);
	else
		call_rcu_tasks_trace(&selem->rcu, __bpf_selem_free_trace_rcu);
}

static void bpf_selem_free_rcu(struct rcu_head *rcu)
{
	struct bpf_local_storage_elem *selem;
	struct bpf_local_storage_map *smap;

	selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
	/* The bpf_local_storage_map_free will wait for rcu_barrier */
	smap = rcu_dereference_check(SDATA(selem)->smap, 1);

	if (smap)
		bpf_obj_free_fields(smap->map.record, SDATA(selem)->data);
	kfree_nolock(selem);
}

static void bpf_selem_free_trace_rcu(struct rcu_head *rcu)
{
	/*
	 * RCU Tasks Trace grace period implies RCU grace period, do
	 * kfree() directly.
	 */
	bpf_selem_free_rcu(rcu);
}

void bpf_selem_free(struct bpf_local_storage_elem *selem,
		    bool reuse_now)
{
	if (!selem->use_kmalloc_nolock) {
		/*
		 * No uptr will be unpin even when reuse_now == false since uptr
		 * is only supported in task local storage, where
		 * smap->use_kmalloc_nolock == true.
		 */
		__bpf_selem_free(selem, reuse_now);
		return;
	}

	if (reuse_now) {
		/*
		 * While it is okay to call bpf_obj_free_fields() that unpins uptr when
		 * reuse_now == true, keep it in bpf_selem_free_rcu() for simplicity.
		 */
		call_rcu(&selem->rcu, bpf_selem_free_rcu);
		return;
	}

	call_rcu_tasks_trace(&selem->rcu, bpf_selem_free_trace_rcu);
}

static void bpf_selem_free_list(struct hlist_head *list, bool reuse_now)
{
	struct bpf_local_storage_elem *selem;
	struct hlist_node *n;

	/* The "_safe" iteration is needed.
	 * The loop is not removing the selem from the list
	 * but bpf_selem_free will use the selem->rcu_head
	 * which is union-ized with the selem->free_node.
	 */
	hlist_for_each_entry_safe(selem, n, list, free_node)
		bpf_selem_free(selem, reuse_now);
}

static void bpf_selem_unlink_storage_nolock_misc(struct bpf_local_storage_elem *selem,
						 struct bpf_local_storage_map *smap,
						 struct bpf_local_storage *local_storage,
						 bool free_local_storage, bool pin_owner)
{
	void *owner = local_storage->owner;
	u32 uncharge = smap->elem_size;

	if (rcu_access_pointer(local_storage->cache[smap->cache_idx]) ==
	    SDATA(selem))
		RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);

	if (pin_owner && !refcount_inc_not_zero(&local_storage->owner_refcnt))
		return;

	uncharge += free_local_storage ? sizeof(*local_storage) : 0;
	mem_uncharge(smap, local_storage->owner, uncharge);
	local_storage->mem_charge -= uncharge;

	if (free_local_storage) {
		local_storage->owner = NULL;

		/* After this RCU_INIT, owner may be freed and cannot be used */
		RCU_INIT_POINTER(*owner_storage(smap, owner), NULL);
	}

	if (pin_owner)
		refcount_dec(&local_storage->owner_refcnt);
}

/* local_storage->lock must be held and selem->local_storage == local_storage.
 * The caller must ensure selem->smap is still valid to be
 * dereferenced for its smap->elem_size and smap->cache_idx.
 */
static bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
					    struct bpf_local_storage_elem *selem,
					    struct hlist_head *free_selem_list)
{
	struct bpf_local_storage_map *smap;
	bool free_local_storage;

	smap = rcu_dereference_check(SDATA(selem)->smap, bpf_rcu_lock_held());

	free_local_storage = hlist_is_singular_node(&selem->snode,
						    &local_storage->list);

	bpf_selem_unlink_storage_nolock_misc(selem, smap, local_storage,
					     free_local_storage, false);

	hlist_del_init_rcu(&selem->snode);

	hlist_add_head(&selem->free_node, free_selem_list);

	return free_local_storage;
}

void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
				   struct bpf_local_storage_elem *selem)
{
	struct bpf_local_storage_map *smap;

	smap = rcu_dereference_check(SDATA(selem)->smap, bpf_rcu_lock_held());
	local_storage->mem_charge += smap->elem_size;

	RCU_INIT_POINTER(selem->local_storage, local_storage);
	hlist_add_head_rcu(&selem->snode, &local_storage->list);
}

static int bpf_selem_unlink_map(struct bpf_local_storage_elem *selem)
{
	struct bpf_local_storage *local_storage;
	struct bpf_local_storage_map *smap;
	struct bpf_local_storage_map_bucket *b;
	unsigned long flags;
	int err;

	local_storage = rcu_dereference_check(selem->local_storage,
					      bpf_rcu_lock_held());
	smap = rcu_dereference_check(SDATA(selem)->smap, bpf_rcu_lock_held());
	b = select_bucket(smap, local_storage);
	err = raw_res_spin_lock_irqsave(&b->lock, flags);
	if (err)
		return err;

	hlist_del_init_rcu(&selem->map_node);
	raw_res_spin_unlock_irqrestore(&b->lock, flags);

	return 0;
}

static void bpf_selem_unlink_map_nolock(struct bpf_local_storage_elem *selem)
{
	hlist_del_init_rcu(&selem->map_node);
}

int bpf_selem_link_map(struct bpf_local_storage_map *smap,
		       struct bpf_local_storage *local_storage,
		       struct bpf_local_storage_elem *selem)
{
	struct bpf_local_storage_map_bucket *b;
	unsigned long flags;
	int err;

	b = select_bucket(smap, local_storage);

	err = raw_res_spin_lock_irqsave(&b->lock, flags);
	if (err)
		return err;

	hlist_add_head_rcu(&selem->map_node, &b->list);
	raw_res_spin_unlock_irqrestore(&b->lock, flags);

	return 0;
}

static void bpf_selem_link_map_nolock(struct bpf_local_storage_map_bucket *b,
				      struct bpf_local_storage_elem *selem)
{
	hlist_add_head_rcu(&selem->map_node, &b->list);
}

/*
 * Unlink an selem from map and local storage with lock held.
 * This is the common path used by local storages to delete an selem.
 */
int bpf_selem_unlink(struct bpf_local_storage_elem *selem)
{
	struct bpf_local_storage *local_storage;
	bool free_local_storage = false;
	HLIST_HEAD(selem_free_list);
	unsigned long flags;
	int err;

	if (unlikely(!selem_linked_to_storage_lockless(selem)))
		/* selem has already been unlinked from sk */
		return 0;

	local_storage = rcu_dereference_check(selem->local_storage,
					      bpf_rcu_lock_held());

	err = raw_res_spin_lock_irqsave(&local_storage->lock, flags);
	if (err)
		return err;

	if (likely(selem_linked_to_storage(selem))) {
		/* Always unlink from map before unlinking from local_storage
		 * because selem will be freed after successfully unlinked from
		 * the local_storage.
		 */
		err = bpf_selem_unlink_map(selem);
		if (err)
			goto out;

		free_local_storage = bpf_selem_unlink_storage_nolock(
			local_storage, selem, &selem_free_list);
	}
out:
	raw_res_spin_unlock_irqrestore(&local_storage->lock, flags);

	bpf_selem_free_list(&selem_free_list, false);

	if (free_local_storage)
		bpf_local_storage_free(local_storage, false);

	return err;
}

/*
 * Unlink an selem from map and local storage with lockless fallback if callers
 * are racing or rqspinlock returns error. It should only be called by
 * bpf_local_storage_destroy() or bpf_local_storage_map_free().
 */
static void bpf_selem_unlink_nofail(struct bpf_local_storage_elem *selem,
				    struct bpf_local_storage_map_bucket *b)
{
	bool in_map_free = !!b, free_storage = false;
	struct bpf_local_storage *local_storage;
	struct bpf_local_storage_map *smap;
	unsigned long flags;
	int err, unlink = 0;

	local_storage = rcu_dereference_check(selem->local_storage, bpf_rcu_lock_held());
	smap = rcu_dereference_check(SDATA(selem)->smap, bpf_rcu_lock_held());

	if (smap) {
		b = b ? : select_bucket(smap, local_storage);
		err = raw_res_spin_lock_irqsave(&b->lock, flags);
		if (!err) {
			/*
			 * Call bpf_obj_free_fields() under b->lock to make sure it is done
			 * exactly once for an selem. Safe to free special fields immediately
			 * as no BPF program should be referencing the selem.
			 */
			if (likely(selem_linked_to_map(selem))) {
				hlist_del_init_rcu(&selem->map_node);
				bpf_obj_free_fields(smap->map.record, SDATA(selem)->data);
				unlink++;
			}
			raw_res_spin_unlock_irqrestore(&b->lock, flags);
		}
		/*
		 * Highly unlikely scenario: resource leak
		 *
		 * When map_free(selem1), destroy(selem1) and destroy(selem2) are racing
		 * and both selem belong to the same bucket, if destroy(selem2) acquired
		 * b->lock and block for too long, neither map_free(selem1) and
		 * destroy(selem1) will be able to free the special field associated
		 * with selem1 as raw_res_spin_lock_irqsave() returns -ETIMEDOUT.
		 */
		WARN_ON_ONCE(err && in_map_free);
		if (!err || in_map_free)
			RCU_INIT_POINTER(SDATA(selem)->smap, NULL);
	}

	if (local_storage) {
		err = raw_res_spin_lock_irqsave(&local_storage->lock, flags);
		if (!err) {
			if (likely(selem_linked_to_storage(selem))) {
				free_storage = hlist_is_singular_node(&selem->snode,
								      &local_storage->list);
				 /*
				  * Okay to skip clearing owner_storage and storage->owner in
				  * destroy() since the owner is going away. No user or bpf
				  * programs should be able to reference it.
				  */
				if (smap && in_map_free)
					bpf_selem_unlink_storage_nolock_misc(
						selem, smap, local_storage,
						free_storage, true);
				hlist_del_init_rcu(&selem->snode);
				unlink++;
			}
			raw_res_spin_unlock_irqrestore(&local_storage->lock, flags);
		}
		if (!err || !in_map_free)
			RCU_INIT_POINTER(selem->local_storage, NULL);
	}

	if (unlink != 2)
		atomic_or(in_map_free ? SELEM_MAP_UNLINKED : SELEM_STORAGE_UNLINKED, &selem->state);

	/*
	 * Normally, an selem can be unlinked under local_storage->lock and b->lock, and
	 * then freed after an RCU grace period. However, if destroy() and map_free() are
	 * racing or rqspinlock returns errors in unlikely situations (unlink != 2), free
	 * the selem only after both map_free() and destroy() see the selem.
	 */
	if (unlink == 2 ||
	    atomic_cmpxchg(&selem->state, SELEM_UNLINKED, SELEM_TOFREE) == SELEM_UNLINKED)
		bpf_selem_free(selem, true);

	if (free_storage)
		bpf_local_storage_free(local_storage, true);
}

void __bpf_local_storage_insert_cache(struct bpf_local_storage *local_storage,
				      struct bpf_local_storage_map *smap,
				      struct bpf_local_storage_elem *selem)
{
	unsigned long flags;
	int err;

	/* spinlock is needed to avoid racing with the
	 * parallel delete.  Otherwise, publishing an already
	 * deleted sdata to the cache will become a use-after-free
	 * problem in the next bpf_local_storage_lookup().
	 */
	err = raw_res_spin_lock_irqsave(&local_storage->lock, flags);
	if (err)
		return;

	if (selem_linked_to_storage(selem))
		rcu_assign_pointer(local_storage->cache[smap->cache_idx], SDATA(selem));
	raw_res_spin_unlock_irqrestore(&local_storage->lock, flags);
}

static int check_flags(const struct bpf_local_storage_data *old_sdata,
		       u64 map_flags)
{
	if (old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_NOEXIST)
		/* elem already exists */
		return -EEXIST;

	if (!old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_EXIST)
		/* elem doesn't exist, cannot update it */
		return -ENOENT;

	return 0;
}

int bpf_local_storage_alloc(void *owner,
			    struct bpf_local_storage_map *smap,
			    struct bpf_local_storage_elem *first_selem,
			    gfp_t gfp_flags)
{
	struct bpf_local_storage *prev_storage, *storage;
	struct bpf_local_storage **owner_storage_ptr;
	struct bpf_local_storage_map_bucket *b;
	unsigned long flags;
	int err;

	err = mem_charge(smap, owner, sizeof(*storage));
	if (err)
		return err;

	if (smap->use_kmalloc_nolock)
		storage = bpf_map_kmalloc_nolock(&smap->map, sizeof(*storage),
						 __GFP_ZERO, NUMA_NO_NODE);
	else
		storage = bpf_map_kzalloc(&smap->map, sizeof(*storage),
					  gfp_flags | __GFP_NOWARN);
	if (!storage) {
		err = -ENOMEM;
		goto uncharge;
	}

	INIT_HLIST_HEAD(&storage->list);
	raw_res_spin_lock_init(&storage->lock);
	storage->owner = owner;
	storage->mem_charge = sizeof(*storage);
	storage->use_kmalloc_nolock = smap->use_kmalloc_nolock;
	refcount_set(&storage->owner_refcnt, 1);

	bpf_selem_link_storage_nolock(storage, first_selem);

	b = select_bucket(smap, storage);
	err = raw_res_spin_lock_irqsave(&b->lock, flags);
	if (err)
		goto uncharge;

	bpf_selem_link_map_nolock(b, first_selem);

	owner_storage_ptr =
		(struct bpf_local_storage **)owner_storage(smap, owner);
	/* Publish storage to the owner.
	 * Instead of using any lock of the kernel object (i.e. owner),
	 * cmpxchg will work with any kernel object regardless what
	 * the running context is, bh, irq...etc.
	 *
	 * From now on, the owner->storage pointer (e.g. sk->sk_bpf_storage)
	 * is protected by the storage->lock.  Hence, when freeing
	 * the owner->storage, the storage->lock must be held before
	 * setting owner->storage ptr to NULL.
	 */
	prev_storage = cmpxchg(owner_storage_ptr, NULL, storage);
	if (unlikely(prev_storage)) {
		bpf_selem_unlink_map_nolock(first_selem);
		raw_res_spin_unlock_irqrestore(&b->lock, flags);
		err = -EAGAIN;
		goto uncharge;
	}
	raw_res_spin_unlock_irqrestore(&b->lock, flags);

	return 0;

uncharge:
	bpf_local_storage_free(storage, true);
	mem_uncharge(smap, owner, sizeof(*storage));
	return err;
}

/* sk cannot be going away because it is linking new elem
 * to sk->sk_bpf_storage. (i.e. sk->sk_refcnt cannot be 0).
 * Otherwise, it will become a leak (and other memory issues
 * during map destruction).
 */
struct bpf_local_storage_data *
bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
			 void *value, u64 map_flags, bool swap_uptrs, gfp_t gfp_flags)
{
	struct bpf_local_storage_data *old_sdata = NULL;
	struct bpf_local_storage_elem *alloc_selem, *selem = NULL;
	struct bpf_local_storage *local_storage;
	struct bpf_local_storage_map_bucket *b;
	HLIST_HEAD(old_selem_free_list);
	unsigned long flags, b_flags;
	int err;

	/* BPF_EXIST and BPF_NOEXIST cannot be both set */
	if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
	    /* BPF_F_LOCK can only be used in a value with spin_lock */
	    unlikely((map_flags & BPF_F_LOCK) &&
		     !btf_record_has_field(smap->map.record, BPF_SPIN_LOCK)))
		return ERR_PTR(-EINVAL);

	if (gfp_flags == GFP_KERNEL && (map_flags & ~BPF_F_LOCK) != BPF_NOEXIST)
		return ERR_PTR(-EINVAL);

	local_storage = rcu_dereference_check(*owner_storage(smap, owner),
					      bpf_rcu_lock_held());
	if (!local_storage || hlist_empty(&local_storage->list)) {
		/* Very first elem for the owner */
		err = check_flags(NULL, map_flags);
		if (err)
			return ERR_PTR(err);

		selem = bpf_selem_alloc(smap, owner, value, swap_uptrs, gfp_flags);
		if (!selem)
			return ERR_PTR(-ENOMEM);

		err = bpf_local_storage_alloc(owner, smap, selem, gfp_flags);
		if (err) {
			bpf_selem_free(selem, true);
			mem_uncharge(smap, owner, smap->elem_size);
			return ERR_PTR(err);
		}

		return SDATA(selem);
	}

	if ((map_flags & BPF_F_LOCK) && !(map_flags & BPF_NOEXIST)) {
		/* Hoping to find an old_sdata to do inline update
		 * such that it can avoid taking the local_storage->lock
		 * and changing the lists.
		 */
		old_sdata =
			bpf_local_storage_lookup(local_storage, smap, false);
		err = check_flags(old_sdata, map_flags);
		if (err)
			return ERR_PTR(err);
		if (old_sdata && selem_linked_to_storage_lockless(SELEM(old_sdata))) {
			copy_map_value_locked(&smap->map, old_sdata->data,
					      value, false);
			return old_sdata;
		}
	}

	/* A lookup has just been done before and concluded a new selem is
	 * needed. The chance of an unnecessary alloc is unlikely.
	 */
	alloc_selem = selem = bpf_selem_alloc(smap, owner, value, swap_uptrs, gfp_flags);
	if (!alloc_selem)
		return ERR_PTR(-ENOMEM);

	err = raw_res_spin_lock_irqsave(&local_storage->lock, flags);
	if (err)
		goto free_selem;

	/* Recheck local_storage->list under local_storage->lock */
	if (unlikely(hlist_empty(&local_storage->list))) {
		/* A parallel del is happening and local_storage is going
		 * away.  It has just been checked before, so very
		 * unlikely.  Return instead of retry to keep things
		 * simple.
		 */
		err = -EAGAIN;
		goto unlock;
	}

	old_sdata = bpf_local_storage_lookup(local_storage, smap, false);
	err = check_flags(old_sdata, map_flags);
	if (err)
		goto unlock;

	if (old_sdata && (map_flags & BPF_F_LOCK)) {
		copy_map_value_locked(&smap->map, old_sdata->data, value,
				      false);
		selem = SELEM(old_sdata);
		goto unlock;
	}

	b = select_bucket(smap, local_storage);

	err = raw_res_spin_lock_irqsave(&b->lock, b_flags);
	if (err)
		goto unlock;

	alloc_selem = NULL;
	/* First, link the new selem to the map */
	bpf_selem_link_map_nolock(b, selem);

	/* Second, link (and publish) the new selem to local_storage */
	bpf_selem_link_storage_nolock(local_storage, selem);

	/* Third, remove old selem, SELEM(old_sdata) */
	if (old_sdata) {
		bpf_selem_unlink_map_nolock(SELEM(old_sdata));
		bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
						&old_selem_free_list);
	}

	raw_res_spin_unlock_irqrestore(&b->lock, b_flags);
unlock:
	raw_res_spin_unlock_irqrestore(&local_storage->lock, flags);
free_selem:
	bpf_selem_free_list(&old_selem_free_list, false);
	if (alloc_selem) {
		mem_uncharge(smap, owner, smap->elem_size);
		bpf_selem_free(alloc_selem, true);
	}
	return err ? ERR_PTR(err) : SDATA(selem);
}

static u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
{
	u64 min_usage = U64_MAX;
	u16 i, res = 0;

	spin_lock(&cache->idx_lock);

	for (i = 0; i < BPF_LOCAL_STORAGE_CACHE_SIZE; i++) {
		if (cache->idx_usage_counts[i] < min_usage) {
			min_usage = cache->idx_usage_counts[i];
			res = i;

			/* Found a free cache_idx */
			if (!min_usage)
				break;
		}
	}
	cache->idx_usage_counts[res]++;

	spin_unlock(&cache->idx_lock);

	return res;
}

static void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
					     u16 idx)
{
	spin_lock(&cache->idx_lock);
	cache->idx_usage_counts[idx]--;
	spin_unlock(&cache->idx_lock);
}

int bpf_local_storage_map_alloc_check(union bpf_attr *attr)
{
	if (attr->map_flags & ~BPF_LOCAL_STORAGE_CREATE_FLAG_MASK ||
	    !(attr->map_flags & BPF_F_NO_PREALLOC) ||
	    attr->max_entries ||
	    attr->key_size != sizeof(int) || !attr->value_size ||
	    /* Enforce BTF for userspace sk dumping */
	    !attr->btf_key_type_id || !attr->btf_value_type_id)
		return -EINVAL;

	if (attr->value_size > BPF_LOCAL_STORAGE_MAX_VALUE_SIZE)
		return -E2BIG;

	return 0;
}

int bpf_local_storage_map_check_btf(struct bpf_map *map,
				    const struct btf *btf,
				    const struct btf_type *key_type,
				    const struct btf_type *value_type)
{
	if (!btf_type_is_i32(key_type))
		return -EINVAL;

	return 0;
}

/*
 * Destroy local storage when the owner is going away. Caller must uncharge memory
 * if memory charging is used.
 */
u32 bpf_local_storage_destroy(struct bpf_local_storage *local_storage)
{
	struct bpf_local_storage_elem *selem;

	/* Neither the bpf_prog nor the bpf_map's syscall
	 * could be modifying the local_storage->list now.
	 * Thus, no elem can be added to or deleted from the
	 * local_storage->list by the bpf_prog or by the bpf_map's syscall.
	 *
	 * It is racing with bpf_local_storage_map_free() alone
	 * when unlinking elem from the local_storage->list and
	 * the map's bucket->list.
	 */
	hlist_for_each_entry_rcu(selem, &local_storage->list, snode)
		bpf_selem_unlink_nofail(selem, NULL);

	if (!refcount_dec_and_test(&local_storage->owner_refcnt)) {
		while (refcount_read(&local_storage->owner_refcnt))
			cpu_relax();
		/*
		 * Paired with refcount_dec() in bpf_selem_unlink_nofail()
		 * to make sure destroy() sees the correct local_storage->mem_charge.
		 */
		smp_mb();
	}

	return local_storage->mem_charge;
}

u64 bpf_local_storage_map_mem_usage(const struct bpf_map *map)
{
	struct bpf_local_storage_map *smap = (struct bpf_local_storage_map *)map;
	u64 usage = sizeof(*smap);

	/* The dynamically callocated selems are not counted currently. */
	usage += sizeof(*smap->buckets) * (1ULL << smap->bucket_log);
	return usage;
}

struct bpf_map *
bpf_local_storage_map_alloc(union bpf_attr *attr,
			    struct bpf_local_storage_cache *cache,
			    bool use_kmalloc_nolock)
{
	struct bpf_local_storage_map *smap;
	unsigned int i;
	u32 nbuckets;
	int err;

	smap = bpf_map_area_alloc(sizeof(*smap), NUMA_NO_NODE);
	if (!smap)
		return ERR_PTR(-ENOMEM);
	bpf_map_init_from_attr(&smap->map, attr);

	nbuckets = roundup_pow_of_two(num_possible_cpus());
	/* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */
	nbuckets = max_t(u32, 2, nbuckets);
	smap->bucket_log = ilog2(nbuckets);

	smap->buckets = bpf_map_kvcalloc(&smap->map, nbuckets,
					 sizeof(*smap->buckets), GFP_USER | __GFP_NOWARN);
	if (!smap->buckets) {
		err = -ENOMEM;
		goto free_smap;
	}

	for (i = 0; i < nbuckets; i++) {
		INIT_HLIST_HEAD(&smap->buckets[i].list);
		raw_res_spin_lock_init(&smap->buckets[i].lock);
	}

	smap->elem_size = offsetof(struct bpf_local_storage_elem,
				   sdata.data[attr->value_size]);

	/* In PREEMPT_RT, kmalloc(GFP_ATOMIC) is still not safe in non
	 * preemptible context. Thus, enforce all storages to use
	 * kmalloc_nolock() when CONFIG_PREEMPT_RT is enabled.
	 */
	smap->use_kmalloc_nolock = IS_ENABLED(CONFIG_PREEMPT_RT) ? true : use_kmalloc_nolock;

	smap->cache_idx = bpf_local_storage_cache_idx_get(cache);
	return &smap->map;

free_smap:
	kvfree(smap->buckets);
	bpf_map_area_free(smap);
	return ERR_PTR(err);
}

void bpf_local_storage_map_free(struct bpf_map *map,
				struct bpf_local_storage_cache *cache)
{
	struct bpf_local_storage_map_bucket *b;
	struct bpf_local_storage_elem *selem;
	struct bpf_local_storage_map *smap;
	unsigned int i;

	smap = (struct bpf_local_storage_map *)map;
	bpf_local_storage_cache_idx_free(cache, smap->cache_idx);

	/* Note that this map might be concurrently cloned from
	 * bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone
	 * RCU read section to finish before proceeding. New RCU
	 * read sections should be prevented via bpf_map_inc_not_zero.
	 */
	synchronize_rcu();

	/* bpf prog and the userspace can no longer access this map
	 * now.  No new selem (of this map) can be added
	 * to the owner->storage or to the map bucket's list.
	 *
	 * The elem of this map can be cleaned up here
	 * or when the storage is freed e.g.
	 * by bpf_sk_storage_free() during __sk_destruct().
	 */
	for (i = 0; i < (1U << smap->bucket_log); i++) {
		b = &smap->buckets[i];

		rcu_read_lock();
		/* No one is adding to b->list now */
restart:
		hlist_for_each_entry_rcu(selem, &b->list, map_node) {
			bpf_selem_unlink_nofail(selem, b);

			if (need_resched()) {
				cond_resched_rcu();
				goto restart;
			}
		}
		rcu_read_unlock();
	}

	/* While freeing the storage we may still need to access the map.
	 *
	 * e.g. when bpf_sk_storage_free() has unlinked selem from the map
	 * which then made the above while((selem = ...)) loop
	 * exit immediately.
	 *
	 * However, while freeing the storage one still needs to access the
	 * smap->elem_size to do the uncharging in
	 * bpf_selem_unlink_storage_nolock().
	 *
	 * Hence, wait another rcu grace period for the storage to be freed.
	 */
	synchronize_rcu();

	/* smap remains in use regardless of kmalloc_nolock, so wait unconditionally. */
	rcu_barrier_tasks_trace();
	rcu_barrier();
	kvfree(smap->buckets);
	bpf_map_area_free(smap);
}