Commit 20b6cc34 authored by Song Liu's avatar Song Liu Committed by Alexei Starovoitov
Browse files

bpf: Avoid hashtab deadlock with map_locked 



If a hashtab is accessed in both non-NMI and NMI context, the system may
deadlock on bucket->lock. Fix this issue with percpu counter map_locked.
map_locked rejects concurrent access to the same bucket from the same CPU.
To reduce memory overhead, map_locked is not added per bucket. Instead,
8 percpu counters are added to each hashtab. buckets are assigned to these
counters based on the lower bits of its hash.

Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201029071925.3103400-3-songliubraving@fb.com
parent c50eb518

kernel/bpf/hashtab.c

+82 −32
Original line number Diff line number Diff line
@@ -86,6 +86,9 @@ struct bucket { 
	};

};



#define HASHTAB_MAP_LOCK_COUNT 8

#define HASHTAB_MAP_LOCK_MASK (HASHTAB_MAP_LOCK_COUNT - 1)



struct bpf_htab {

	struct bpf_map map;

	struct bucket *buckets;
@@ -100,6 +103,7 @@ struct bpf_htab { 
	u32 elem_size;	/* size of each element in bytes */

	u32 hashrnd;

	struct lock_class_key lockdep_key;

	int __percpu *map_locked[HASHTAB_MAP_LOCK_COUNT];

};



/* each htab element is struct htab_elem + key + value */
@@ -152,26 +156,41 @@ static void htab_init_buckets(struct bpf_htab *htab) 
	}

}



static inline unsigned long htab_lock_bucket(const struct bpf_htab *htab,

					     struct bucket *b)

static inline int htab_lock_bucket(const struct bpf_htab *htab,

				   struct bucket *b, u32 hash,

				   unsigned long *pflags)

{

	unsigned long flags;



	hash = hash & HASHTAB_MAP_LOCK_MASK;



	migrate_disable();

	if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {

		__this_cpu_dec(*(htab->map_locked[hash]));

		migrate_enable();

		return -EBUSY;

	}



	if (htab_use_raw_lock(htab))

		raw_spin_lock_irqsave(&b->raw_lock, flags);

	else

		spin_lock_irqsave(&b->lock, flags);

	return flags;

	*pflags = flags;



	return 0;

}



static inline void htab_unlock_bucket(const struct bpf_htab *htab,

				      struct bucket *b,

				      struct bucket *b, u32 hash,

				      unsigned long flags)

{

	hash = hash & HASHTAB_MAP_LOCK_MASK;

	if (htab_use_raw_lock(htab))

		raw_spin_unlock_irqrestore(&b->raw_lock, flags);

	else

		spin_unlock_irqrestore(&b->lock, flags);

	__this_cpu_dec(*(htab->map_locked[hash]));

	migrate_enable();

}



static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node);
@@ -429,8 +448,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
	bool percpu_lru = (attr->map_flags & BPF_F_NO_COMMON_LRU);

	bool prealloc = !(attr->map_flags & BPF_F_NO_PREALLOC);

	struct bpf_htab *htab;

	int err, i;

	u64 cost;

	int err;



	htab = kzalloc(sizeof(*htab), GFP_USER);

	if (!htab)
@@ -487,6 +506,13 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
	if (!htab->buckets)

		goto free_charge;



	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++) {

		htab->map_locked[i] = __alloc_percpu_gfp(sizeof(int),

							 sizeof(int), GFP_USER);

		if (!htab->map_locked[i])

			goto free_map_locked;

	}



	if (htab->map.map_flags & BPF_F_ZERO_SEED)

		htab->hashrnd = 0;

	else
@@ -497,7 +523,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
	if (prealloc) {

		err = prealloc_init(htab);

		if (err)

			goto free_buckets;

			goto free_map_locked;



		if (!percpu && !lru) {

			/* lru itself can remove the least used element, so
@@ -513,7 +539,9 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 


free_prealloc:

	prealloc_destroy(htab);

free_buckets:

free_map_locked:

	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)

		free_percpu(htab->map_locked[i]);

	bpf_map_area_free(htab->buckets);

free_charge:

	bpf_map_charge_finish(&htab->map.memory);
@@ -694,12 +722,15 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node) 
	struct hlist_nulls_node *n;

	unsigned long flags;

	struct bucket *b;

	int ret;



	tgt_l = container_of(node, struct htab_elem, lru_node);

	b = __select_bucket(htab, tgt_l->hash);

	head = &b->head;



	flags = htab_lock_bucket(htab, b);

	ret = htab_lock_bucket(htab, b, tgt_l->hash, &flags);

	if (ret)

		return false;



	hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)

		if (l == tgt_l) {
@@ -707,7 +738,7 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node) 
			break;

		}



	htab_unlock_bucket(htab, b, flags);

	htab_unlock_bucket(htab, b, tgt_l->hash, flags);



	return l == tgt_l;

}
@@ -979,7 +1010,9 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, 
		 */

	}



	flags = htab_lock_bucket(htab, b);

	ret = htab_lock_bucket(htab, b, hash, &flags);

	if (ret)

		return ret;



	l_old = lookup_elem_raw(head, hash, key, key_size);
@@ -1020,7 +1053,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, 
	}

	ret = 0;

err:

	htab_unlock_bucket(htab, b, flags);

	htab_unlock_bucket(htab, b, hash, flags);

	return ret;

}
@@ -1058,7 +1091,9 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value, 
		return -ENOMEM;

	memcpy(l_new->key + round_up(map->key_size, 8), value, map->value_size);



	flags = htab_lock_bucket(htab, b);

	ret = htab_lock_bucket(htab, b, hash, &flags);

	if (ret)

		return ret;



	l_old = lookup_elem_raw(head, hash, key, key_size);
@@ -1077,7 +1112,7 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value, 
	ret = 0;



err:

	htab_unlock_bucket(htab, b, flags);

	htab_unlock_bucket(htab, b, hash, flags);



	if (ret)

		bpf_lru_push_free(&htab->lru, &l_new->lru_node);
@@ -1112,7 +1147,9 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key, 
	b = __select_bucket(htab, hash);

	head = &b->head;



	flags = htab_lock_bucket(htab, b);

	ret = htab_lock_bucket(htab, b, hash, &flags);

	if (ret)

		return ret;



	l_old = lookup_elem_raw(head, hash, key, key_size);
@@ -1135,7 +1172,7 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key, 
	}

	ret = 0;

err:

	htab_unlock_bucket(htab, b, flags);

	htab_unlock_bucket(htab, b, hash, flags);

	return ret;

}
@@ -1175,7 +1212,9 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key, 
			return -ENOMEM;

	}



	flags = htab_lock_bucket(htab, b);

	ret = htab_lock_bucket(htab, b, hash, &flags);

	if (ret)

		return ret;



	l_old = lookup_elem_raw(head, hash, key, key_size);
@@ -1197,7 +1236,7 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key, 
	}

	ret = 0;

err:

	htab_unlock_bucket(htab, b, flags);

	htab_unlock_bucket(htab, b, hash, flags);

	if (l_new)

		bpf_lru_push_free(&htab->lru, &l_new->lru_node);

	return ret;
@@ -1225,7 +1264,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key) 
	struct htab_elem *l;

	unsigned long flags;

	u32 hash, key_size;

	int ret = -ENOENT;

	int ret;



	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
@@ -1235,17 +1274,20 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key) 
	b = __select_bucket(htab, hash);

	head = &b->head;



	flags = htab_lock_bucket(htab, b);

	ret = htab_lock_bucket(htab, b, hash, &flags);

	if (ret)

		return ret;



	l = lookup_elem_raw(head, hash, key, key_size);



	if (l) {

		hlist_nulls_del_rcu(&l->hash_node);

		free_htab_elem(htab, l);

		ret = 0;

	} else {

		ret = -ENOENT;

	}



	htab_unlock_bucket(htab, b, flags);

	htab_unlock_bucket(htab, b, hash, flags);

	return ret;

}
@@ -1257,7 +1299,7 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key) 
	struct htab_elem *l;

	unsigned long flags;

	u32 hash, key_size;

	int ret = -ENOENT;

	int ret;



	WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
@@ -1267,16 +1309,18 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key) 
	b = __select_bucket(htab, hash);

	head = &b->head;



	flags = htab_lock_bucket(htab, b);

	ret = htab_lock_bucket(htab, b, hash, &flags);

	if (ret)

		return ret;



	l = lookup_elem_raw(head, hash, key, key_size);



	if (l) {

	if (l)

		hlist_nulls_del_rcu(&l->hash_node);

		ret = 0;

	}

	else

		ret = -ENOENT;



	htab_unlock_bucket(htab, b, flags);

	htab_unlock_bucket(htab, b, hash, flags);

	if (l)

		bpf_lru_push_free(&htab->lru, &l->lru_node);

	return ret;
@@ -1302,6 +1346,7 @@ static void delete_all_elements(struct bpf_htab *htab) 
static void htab_map_free(struct bpf_map *map)

{

	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);

	int i;



	/* bpf_free_used_maps() or close(map_fd) will trigger this map_free callback.

	 * bpf_free_used_maps() is called after bpf prog is no longer executing.
@@ -1320,6 +1365,8 @@ static void htab_map_free(struct bpf_map *map) 
	free_percpu(htab->extra_elems);

	bpf_map_area_free(htab->buckets);

	lockdep_unregister_key(&htab->lockdep_key);

	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)

		free_percpu(htab->map_locked[i]);

	kfree(htab);

}
@@ -1423,8 +1470,11 @@ again_nocopy: 
	b = &htab->buckets[batch];

	head = &b->head;

	/* do not grab the lock unless need it (bucket_cnt > 0). */

	if (locked)

		flags = htab_lock_bucket(htab, b);

	if (locked) {

		ret = htab_lock_bucket(htab, b, batch, &flags);

		if (ret)

			goto next_batch;

	}



	bucket_cnt = 0;

	hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)
@@ -1441,7 +1491,7 @@ again_nocopy: 
		/* Note that since bucket_cnt > 0 here, it is implicit

		 * that the locked was grabbed, so release it.

		 */

		htab_unlock_bucket(htab, b, flags);

		htab_unlock_bucket(htab, b, batch, flags);

		rcu_read_unlock();

		bpf_enable_instrumentation();

		goto after_loop;
@@ -1452,7 +1502,7 @@ again_nocopy: 
		/* Note that since bucket_cnt > 0 here, it is implicit

		 * that the locked was grabbed, so release it.

		 */

		htab_unlock_bucket(htab, b, flags);

		htab_unlock_bucket(htab, b, batch, flags);

		rcu_read_unlock();

		bpf_enable_instrumentation();

		kvfree(keys);
@@ -1505,7 +1555,7 @@ again_nocopy: 
		dst_val += value_size;

	}



	htab_unlock_bucket(htab, b, flags);

	htab_unlock_bucket(htab, b, batch, flags);

	locked = false;



	while (node_to_free) {

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