bpf: Split bpf_local_storage to bpf_sk_storage (450af8d0) · Commits · EulixOS / Software / Kernel

include/linux/bpf_local_storage.h

0 → 100644

+163 −0

Original line number	Diff line number	Diff line
		/* SPDX-License-Identifier: GPL-2.0 */
		/*
		* Copyright (c) 2019 Facebook
		* Copyright 2020 Google LLC.
		*/

		#ifndef _BPF_LOCAL_STORAGE_H
		#define _BPF_LOCAL_STORAGE_H

		#include <linux/bpf.h>
		#include <linux/rculist.h>
		#include <linux/list.h>
		#include <linux/hash.h>
		#include <linux/types.h>
		#include <uapi/linux/btf.h>

		#define BPF_LOCAL_STORAGE_CACHE_SIZE 16

		struct bpf_local_storage_map_bucket {
		struct hlist_head list;
		raw_spinlock_t lock;
		};

		/* Thp map is not the primary owner of a bpf_local_storage_elem.
		* Instead, the container object (eg. sk->sk_bpf_storage) is.
		*
		* The map (bpf_local_storage_map) is for two purposes
		* 1. Define the size of the "local storage". It is
		* the map's value_size.
		*
		* 2. Maintain a list to keep track of all elems such
		* that they can be cleaned up during the map destruction.
		*
		* When a bpf local storage is being looked up for a
		* particular object, the "bpf_map" pointer is actually used
		* as the "key" to search in the list of elem in
		* the respective bpf_local_storage owned by the object.
		*
		* e.g. sk->sk_bpf_storage is the mini-map with the "bpf_map" pointer
		* as the searching key.
		*/
		struct bpf_local_storage_map {
		struct bpf_map map;
		/* Lookup elem does not require accessing the map.
		*
		* Updating/Deleting requires a bucket lock to
		* link/unlink the elem from the map. Having
		* multiple buckets to improve contention.
		*/
		struct bpf_local_storage_map_bucket *buckets;
		u32 bucket_log;
		u16 elem_size;
		u16 cache_idx;
		};

		struct bpf_local_storage_data {
		/* smap is used as the searching key when looking up
		* from the object's bpf_local_storage.
		*
		* Put it in the same cacheline as the data to minimize
		* the number of cachelines access during the cache hit case.
		*/
		struct bpf_local_storage_map __rcu *smap;
		u8 data[] __aligned(8);
		};

		/* Linked to bpf_local_storage and bpf_local_storage_map */
		struct bpf_local_storage_elem {
		struct hlist_node map_node; /* Linked to bpf_local_storage_map */
		struct hlist_node snode; /* Linked to bpf_local_storage */
		struct bpf_local_storage __rcu *local_storage;
		struct rcu_head rcu;
		/* 8 bytes hole */
		/* The data is stored in aother cacheline to minimize
		* the number of cachelines access during a cache hit.
		*/
		struct bpf_local_storage_data sdata ____cacheline_aligned;
		};

		struct bpf_local_storage {
		struct bpf_local_storage_data __rcu *cache[BPF_LOCAL_STORAGE_CACHE_SIZE];
		struct hlist_head list; /* List of bpf_local_storage_elem */
		void owner; / The object that owns the above "list" of
		* bpf_local_storage_elem.
		*/
		struct rcu_head rcu;
		raw_spinlock_t lock; /* Protect adding/removing from the "list" */
		};

		/* U16_MAX is much more than enough for sk local storage
		* considering a tcp_sock is ~2k.
		*/
		#define BPF_LOCAL_STORAGE_MAX_VALUE_SIZE \
		min_t(u32, \
		(KMALLOC_MAX_SIZE - MAX_BPF_STACK - \
		sizeof(struct bpf_local_storage_elem)), \
		(U16_MAX - sizeof(struct bpf_local_storage_elem)))

		#define SELEM(_SDATA) \
		container_of((_SDATA), struct bpf_local_storage_elem, sdata)
		#define SDATA(_SELEM) (&(_SELEM)->sdata)

		#define BPF_LOCAL_STORAGE_CACHE_SIZE 16

		struct bpf_local_storage_cache {
		spinlock_t idx_lock;
		u64 idx_usage_counts[BPF_LOCAL_STORAGE_CACHE_SIZE];
		};

		#define DEFINE_BPF_STORAGE_CACHE(name) \
		static struct bpf_local_storage_cache name = { \
		.idx_lock = __SPIN_LOCK_UNLOCKED(name.idx_lock), \
		}

		u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache);
		void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
		u16 idx);

		/* Helper functions for bpf_local_storage */
		int bpf_local_storage_map_alloc_check(union bpf_attr *attr);

		struct bpf_local_storage_map bpf_local_storage_map_alloc(union bpf_attr attr);

		struct bpf_local_storage_data *
		bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
		struct bpf_local_storage_map *smap,
		bool cacheit_lockit);

		void bpf_local_storage_map_free(struct bpf_local_storage_map *smap);

		int bpf_local_storage_map_check_btf(const struct bpf_map *map,
		const struct btf *btf,
		const struct btf_type *key_type,
		const struct btf_type *value_type);

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

		bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
		struct bpf_local_storage_elem *selem,
		bool uncharge_omem);

		void bpf_selem_unlink(struct bpf_local_storage_elem *selem);

		void bpf_selem_link_map(struct bpf_local_storage_map *smap,
		struct bpf_local_storage_elem *selem);

		void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem);

		struct bpf_local_storage_elem *
		bpf_selem_alloc(struct bpf_local_storage_map smap, void owner, void *value,
		bool charge_mem);

		int
		bpf_local_storage_alloc(void *owner,
		struct bpf_local_storage_map *smap,
		struct bpf_local_storage_elem *first_selem);

		struct bpf_local_storage_data *
		bpf_local_storage_update(void owner, struct bpf_local_storage_map smap,
		void *value, u64 map_flags);

		#endif /* _BPF_LOCAL_STORAGE_H */

include/net/bpf_sk_storage.h

+1 −60

Original line number	Diff line number	Diff line
		@@ -12,6 +12,7 @@
		#include <net/sock.h>
		#include <uapi/linux/sock_diag.h>
		#include <uapi/linux/btf.h>
		#include <linux/bpf_local_storage.h>

		struct sock;

		@@ -26,66 +27,6 @@ struct sk_buff;
		struct nlattr;
		struct sock;

		#define BPF_LOCAL_STORAGE_CACHE_SIZE 16

		struct bpf_local_storage_cache {
		spinlock_t idx_lock;
		u64 idx_usage_counts[BPF_LOCAL_STORAGE_CACHE_SIZE];
		};

		#define DEFINE_BPF_STORAGE_CACHE(name) \
		static struct bpf_local_storage_cache name = { \
		.idx_lock = __SPIN_LOCK_UNLOCKED(name.idx_lock), \
		}

		u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache);
		void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
		u16 idx);

		/* Helper functions for bpf_local_storage */
		int bpf_local_storage_map_alloc_check(union bpf_attr *attr);

		struct bpf_local_storage_map bpf_local_storage_map_alloc(union bpf_attr attr);

		struct bpf_local_storage_data *
		bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
		struct bpf_local_storage_map *smap,
		bool cacheit_lockit);

		void bpf_local_storage_map_free(struct bpf_local_storage_map *smap);

		int bpf_local_storage_map_check_btf(const struct bpf_map *map,
		const struct btf *btf,
		const struct btf_type *key_type,
		const struct btf_type *value_type);

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

		bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
		struct bpf_local_storage_elem *selem,
		bool uncharge_omem);

		void bpf_selem_unlink(struct bpf_local_storage_elem *selem);

		void bpf_selem_link_map(struct bpf_local_storage_map *smap,
		struct bpf_local_storage_elem *selem);

		void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem);

		struct bpf_local_storage_elem *
		bpf_selem_alloc(struct bpf_local_storage_map smap, void owner, void *value,
		bool charge_mem);

		int
		bpf_local_storage_alloc(void *owner,
		struct bpf_local_storage_map *smap,
		struct bpf_local_storage_elem *first_selem);

		struct bpf_local_storage_data *
		bpf_local_storage_update(void owner, struct bpf_local_storage_map smap,
		void *value, u64 map_flags);

		#ifdef CONFIG_BPF_SYSCALL
		int bpf_sk_storage_clone(const struct sock sk, struct sock newsk);
		struct bpf_sk_storage_diag *

kernel/bpf/Makefile

+1 −0

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		@@ -12,6 +12,7 @@ obj-$(CONFIG_BPF_JIT) += dispatcher.o
		ifeq ($(CONFIG_NET),y)
		obj-$(CONFIG_BPF_SYSCALL) += devmap.o
		obj-$(CONFIG_BPF_SYSCALL) += cpumap.o
		obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o
		obj-$(CONFIG_BPF_SYSCALL) += offload.o
		obj-$(CONFIG_BPF_SYSCALL) += net_namespace.o
		endif

kernel/bpf/bpf_local_storage.c

0 → 100644

+600 −0

Original line number	Diff line number	Diff line
		// 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>

		#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_elem *selem)
		{
		return &smap->buckets[hash_ptr(selem, 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(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 charge_mem)
		{
		struct bpf_local_storage_elem *selem;

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

		selem = kzalloc(smap->elem_size, GFP_ATOMIC \| __GFP_NOWARN);
		if (selem) {
		if (value)
		memcpy(SDATA(selem)->data, value, smap->map.value_size);
		return selem;
		}

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

		return NULL;
		}

		/* 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.
		*/
		bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
		struct bpf_local_storage_elem *selem,
		bool uncharge_mem)
		{
		struct bpf_local_storage_map *smap;
		bool free_local_storage;
		void *owner;

		smap = rcu_dereference(SDATA(selem)->smap);
		owner = local_storage->owner;

		/* All uncharging on the owner must be done first.
		* The owner may be freed once the last selem is unlinked
		* from local_storage.
		*/
		if (uncharge_mem)
		mem_uncharge(smap, owner, smap->elem_size);

		free_local_storage = hlist_is_singular_node(&selem->snode,
		&local_storage->list);
		if (free_local_storage) {
		mem_uncharge(smap, owner, sizeof(struct bpf_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);

		/* local_storage is not freed now. local_storage->lock is
		* still held and raw_spin_unlock_bh(&local_storage->lock)
		* will be done by the caller.
		*
		* Although the unlock will be done under
		* rcu_read_lock(), it is more intutivie to
		* read if kfree_rcu(local_storage, rcu) is done
		* after the raw_spin_unlock_bh(&local_storage->lock).
		*
		* Hence, a "bool free_local_storage" is returned
		* to the caller which then calls the kfree_rcu()
		* after unlock.
		*/
		}
		hlist_del_init_rcu(&selem->snode);
		if (rcu_access_pointer(local_storage->cache[smap->cache_idx]) ==
		SDATA(selem))
		RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);

		kfree_rcu(selem, rcu);

		return free_local_storage;
		}

		static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
		{
		struct bpf_local_storage *local_storage;
		bool free_local_storage = false;

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

		local_storage = rcu_dereference(selem->local_storage);
		raw_spin_lock_bh(&local_storage->lock);
		if (likely(selem_linked_to_storage(selem)))
		free_local_storage = bpf_selem_unlink_storage_nolock(
		local_storage, selem, true);
		raw_spin_unlock_bh(&local_storage->lock);

		if (free_local_storage)
		kfree_rcu(local_storage, rcu);
		}

		void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
		struct bpf_local_storage_elem *selem)
		{
		RCU_INIT_POINTER(selem->local_storage, local_storage);
		hlist_add_head(&selem->snode, &local_storage->list);
		}

		void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem)
		{
		struct bpf_local_storage_map *smap;
		struct bpf_local_storage_map_bucket *b;

		if (unlikely(!selem_linked_to_map(selem)))
		/* selem has already be unlinked from smap */
		return;

		smap = rcu_dereference(SDATA(selem)->smap);
		b = select_bucket(smap, selem);
		raw_spin_lock_bh(&b->lock);
		if (likely(selem_linked_to_map(selem)))
		hlist_del_init_rcu(&selem->map_node);
		raw_spin_unlock_bh(&b->lock);
		}

		void bpf_selem_link_map(struct bpf_local_storage_map *smap,
		struct bpf_local_storage_elem *selem)
		{
		struct bpf_local_storage_map_bucket *b = select_bucket(smap, selem);

		raw_spin_lock_bh(&b->lock);
		RCU_INIT_POINTER(SDATA(selem)->smap, smap);
		hlist_add_head_rcu(&selem->map_node, &b->list);
		raw_spin_unlock_bh(&b->lock);
		}

		void bpf_selem_unlink(struct bpf_local_storage_elem *selem)
		{
		/* Always unlink from map before unlinking from local_storage
		* because selem will be freed after successfully unlinked from
		* the local_storage.
		*/
		bpf_selem_unlink_map(selem);
		__bpf_selem_unlink_storage(selem);
		}

		struct bpf_local_storage_data *
		bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
		struct bpf_local_storage_map *smap,
		bool cacheit_lockit)
		{
		struct bpf_local_storage_data *sdata;
		struct bpf_local_storage_elem *selem;

		/* Fast path (cache hit) */
		sdata = rcu_dereference(local_storage->cache[smap->cache_idx]);
		if (sdata && rcu_access_pointer(sdata->smap) == smap)
		return sdata;

		/* Slow path (cache miss) */
		hlist_for_each_entry_rcu(selem, &local_storage->list, snode)
		if (rcu_access_pointer(SDATA(selem)->smap) == smap)
		break;

		if (!selem)
		return NULL;

		sdata = SDATA(selem);
		if (cacheit_lockit) {
		/* 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().
		*/
		raw_spin_lock_bh(&local_storage->lock);
		if (selem_linked_to_storage(selem))
		rcu_assign_pointer(local_storage->cache[smap->cache_idx],
		sdata);
		raw_spin_unlock_bh(&local_storage->lock);
		}

		return sdata;
		}

		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)
		{
		struct bpf_local_storage prev_storage, storage;
		struct bpf_local_storage **owner_storage_ptr;
		int err;

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

		storage = kzalloc(sizeof(*storage), GFP_ATOMIC \| __GFP_NOWARN);
		if (!storage) {
		err = -ENOMEM;
		goto uncharge;
		}

		INIT_HLIST_HEAD(&storage->list);
		raw_spin_lock_init(&storage->lock);
		storage->owner = owner;

		bpf_selem_link_storage_nolock(storage, first_selem);
		bpf_selem_link_map(smap, 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(first_selem);
		err = -EAGAIN;
		goto uncharge;

		/* Note that even first_selem was linked to smap's
		* bucket->list, first_selem can be freed immediately
		* (instead of kfree_rcu) because
		* bpf_local_storage_map_free() does a
		* synchronize_rcu() before walking the bucket->list.
		* Hence, no one is accessing selem from the
		* bucket->list under rcu_read_lock().
		*/
		}

		return 0;

		uncharge:
		kfree(storage);
		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)
		{
		struct bpf_local_storage_data *old_sdata = NULL;
		struct bpf_local_storage_elem *selem;
		struct bpf_local_storage *local_storage;
		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) &&
		!map_value_has_spin_lock(&smap->map)))
		return ERR_PTR(-EINVAL);

		local_storage = rcu_dereference(*owner_storage(smap, owner));
		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, true);
		if (!selem)
		return ERR_PTR(-ENOMEM);

		err = bpf_local_storage_alloc(owner, smap, selem);
		if (err) {
		kfree(selem);
		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(SELEM(old_sdata))) {
		copy_map_value_locked(&smap->map, old_sdata->data,
		value, false);
		return old_sdata;
		}
		}

		raw_spin_lock_bh(&local_storage->lock);

		/* 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_err;
		}

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

		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;
		}

		/* local_storage->lock is held. Hence, we are sure
		* we can unlink and uncharge the old_sdata successfully
		* later. Hence, instead of charging the new selem now
		* and then uncharge the old selem later (which may cause
		* a potential but unnecessary charge failure), avoid taking
		* a charge at all here (the "!old_sdata" check) and the
		* old_sdata will not be uncharged later during
		* bpf_selem_unlink_storage_nolock().
		*/
		selem = bpf_selem_alloc(smap, owner, value, !old_sdata);
		if (!selem) {
		err = -ENOMEM;
		goto unlock_err;
		}

		/* First, link the new selem to the map */
		bpf_selem_link_map(smap, 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(SELEM(old_sdata));
		bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
		false);
		}

		unlock:
		raw_spin_unlock_bh(&local_storage->lock);
		return SDATA(selem);

		unlock_err:
		raw_spin_unlock_bh(&local_storage->lock);
		return ERR_PTR(err);
		}

		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;
		}

		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);
		}

		void bpf_local_storage_map_free(struct bpf_local_storage_map *smap)
		{
		struct bpf_local_storage_elem *selem;
		struct bpf_local_storage_map_bucket *b;
		unsigned int i;

		/* 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 */
		while ((selem = hlist_entry_safe(
		rcu_dereference_raw(hlist_first_rcu(&b->list)),
		struct bpf_local_storage_elem, map_node))) {
		bpf_selem_unlink(selem);
		cond_resched_rcu();
		}
		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();

		kvfree(smap->buckets);
		kfree(smap);
		}

		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 (!bpf_capable())
		return -EPERM;

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

		return 0;
		}

		struct bpf_local_storage_map bpf_local_storage_map_alloc(union bpf_attr attr)
		{
		struct bpf_local_storage_map *smap;
		unsigned int i;
		u32 nbuckets;
		u64 cost;
		int ret;

		smap = kzalloc(sizeof(*smap), GFP_USER \| __GFP_NOWARN);
		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);
		cost = sizeof(smap->buckets) nbuckets + sizeof(*smap);

		ret = bpf_map_charge_init(&smap->map.memory, cost);
		if (ret < 0) {
		kfree(smap);
		return ERR_PTR(ret);
		}

		smap->buckets = kvcalloc(sizeof(*smap->buckets), nbuckets,
		GFP_USER \| __GFP_NOWARN);
		if (!smap->buckets) {
		bpf_map_charge_finish(&smap->map.memory);
		kfree(smap);
		return ERR_PTR(-ENOMEM);
		}

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

		smap->elem_size =
		sizeof(struct bpf_local_storage_elem) + attr->value_size;

		return smap;
		}

		int bpf_local_storage_map_check_btf(const struct bpf_map *map,
		const struct btf *btf,
		const struct btf_type *key_type,
		const struct btf_type *value_type)
		{
		u32 int_data;

		if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
		return -EINVAL;

		int_data = (u32 )(key_type + 1);
		if (BTF_INT_BITS(int_data) != 32 \|\| BTF_INT_OFFSET(int_data))
		return -EINVAL;

		return 0;
		}

net/core/bpf_sk_storage.c

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