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: Song Liu <songliubraving@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20201029071925.3103400-3-songliubraving@fb.com
This commit is contained in:
Song Liu
Alexei Starovoitov
Родитель
c50eb518e2
Коммит
20b6cc34ea
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@ -86,6 +86,9 @@ struct bucket {
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};
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};
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#define HASHTAB_MAP_LOCK_COUNT 8
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#define HASHTAB_MAP_LOCK_MASK (HASHTAB_MAP_LOCK_COUNT - 1)
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struct bpf_htab {
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struct bpf_map map;
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struct bucket *buckets;
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@ -100,6 +103,7 @@ struct bpf_htab {
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u32 elem_size; /* size of each element in bytes */
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u32 hashrnd;
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struct lock_class_key lockdep_key;
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int __percpu *map_locked[HASHTAB_MAP_LOCK_COUNT];
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};
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/* each htab element is struct htab_elem + key + value */
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@ -152,26 +156,41 @@ static void htab_init_buckets(struct bpf_htab *htab)
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}
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}
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static inline unsigned long htab_lock_bucket(const struct bpf_htab *htab,
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struct bucket *b)
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static inline int htab_lock_bucket(const struct bpf_htab *htab,
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struct bucket *b, u32 hash,
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unsigned long *pflags)
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{
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unsigned long flags;
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hash = hash & HASHTAB_MAP_LOCK_MASK;
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migrate_disable();
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if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {
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__this_cpu_dec(*(htab->map_locked[hash]));
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migrate_enable();
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return -EBUSY;
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}
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if (htab_use_raw_lock(htab))
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raw_spin_lock_irqsave(&b->raw_lock, flags);
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else
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spin_lock_irqsave(&b->lock, flags);
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return flags;
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*pflags = flags;
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return 0;
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}
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static inline void htab_unlock_bucket(const struct bpf_htab *htab,
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struct bucket *b,
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struct bucket *b, u32 hash,
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unsigned long flags)
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{
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hash = hash & HASHTAB_MAP_LOCK_MASK;
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if (htab_use_raw_lock(htab))
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raw_spin_unlock_irqrestore(&b->raw_lock, flags);
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else
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spin_unlock_irqrestore(&b->lock, flags);
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__this_cpu_dec(*(htab->map_locked[hash]));
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migrate_enable();
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}
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static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node);
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@ -429,8 +448,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
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bool percpu_lru = (attr->map_flags & BPF_F_NO_COMMON_LRU);
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bool prealloc = !(attr->map_flags & BPF_F_NO_PREALLOC);
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struct bpf_htab *htab;
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int err, i;
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u64 cost;
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int err;
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htab = kzalloc(sizeof(*htab), GFP_USER);
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if (!htab)
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@ -487,6 +506,13 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
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if (!htab->buckets)
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goto free_charge;
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for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++) {
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htab->map_locked[i] = __alloc_percpu_gfp(sizeof(int),
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sizeof(int), GFP_USER);
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if (!htab->map_locked[i])
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goto free_map_locked;
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}
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if (htab->map.map_flags & BPF_F_ZERO_SEED)
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htab->hashrnd = 0;
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else
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@ -497,7 +523,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
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if (prealloc) {
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err = prealloc_init(htab);
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if (err)
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goto free_buckets;
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goto free_map_locked;
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if (!percpu && !lru) {
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/* lru itself can remove the least used element, so
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@ -513,7 +539,9 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
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free_prealloc:
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prealloc_destroy(htab);
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free_buckets:
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free_map_locked:
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for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
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free_percpu(htab->map_locked[i]);
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bpf_map_area_free(htab->buckets);
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free_charge:
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bpf_map_charge_finish(&htab->map.memory);
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@ -694,12 +722,15 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node)
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struct hlist_nulls_node *n;
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unsigned long flags;
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struct bucket *b;
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int ret;
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tgt_l = container_of(node, struct htab_elem, lru_node);
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b = __select_bucket(htab, tgt_l->hash);
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head = &b->head;
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flags = htab_lock_bucket(htab, b);
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ret = htab_lock_bucket(htab, b, tgt_l->hash, &flags);
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if (ret)
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return false;
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hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)
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if (l == tgt_l) {
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@ -707,7 +738,7 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node)
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break;
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}
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, tgt_l->hash, flags);
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return l == tgt_l;
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}
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@ -979,7 +1010,9 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
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*/
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}
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flags = htab_lock_bucket(htab, b);
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ret = htab_lock_bucket(htab, b, hash, &flags);
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if (ret)
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return ret;
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l_old = lookup_elem_raw(head, hash, key, key_size);
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@ -1020,7 +1053,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
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}
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ret = 0;
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err:
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, hash, flags);
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return ret;
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}
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@ -1058,7 +1091,9 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
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return -ENOMEM;
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memcpy(l_new->key + round_up(map->key_size, 8), value, map->value_size);
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flags = htab_lock_bucket(htab, b);
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ret = htab_lock_bucket(htab, b, hash, &flags);
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if (ret)
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return ret;
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l_old = lookup_elem_raw(head, hash, key, key_size);
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@ -1077,7 +1112,7 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
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ret = 0;
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err:
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, hash, flags);
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if (ret)
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bpf_lru_push_free(&htab->lru, &l_new->lru_node);
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@ -1112,7 +1147,9 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
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b = __select_bucket(htab, hash);
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head = &b->head;
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flags = htab_lock_bucket(htab, b);
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ret = htab_lock_bucket(htab, b, hash, &flags);
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if (ret)
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return ret;
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l_old = lookup_elem_raw(head, hash, key, key_size);
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@ -1135,7 +1172,7 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
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}
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ret = 0;
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err:
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, hash, flags);
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return ret;
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}
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@ -1175,7 +1212,9 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
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return -ENOMEM;
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}
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flags = htab_lock_bucket(htab, b);
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ret = htab_lock_bucket(htab, b, hash, &flags);
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if (ret)
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return ret;
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l_old = lookup_elem_raw(head, hash, key, key_size);
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@ -1197,7 +1236,7 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
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}
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ret = 0;
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err:
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, hash, flags);
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if (l_new)
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bpf_lru_push_free(&htab->lru, &l_new->lru_node);
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return ret;
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@ -1225,7 +1264,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
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struct htab_elem *l;
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unsigned long flags;
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u32 hash, key_size;
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int ret = -ENOENT;
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int ret;
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WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
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@ -1235,17 +1274,20 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
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b = __select_bucket(htab, hash);
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head = &b->head;
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flags = htab_lock_bucket(htab, b);
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ret = htab_lock_bucket(htab, b, hash, &flags);
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if (ret)
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return ret;
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l = lookup_elem_raw(head, hash, key, key_size);
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if (l) {
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hlist_nulls_del_rcu(&l->hash_node);
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free_htab_elem(htab, l);
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ret = 0;
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} else {
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ret = -ENOENT;
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}
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, hash, flags);
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return ret;
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}
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@ -1257,7 +1299,7 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key)
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struct htab_elem *l;
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unsigned long flags;
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u32 hash, key_size;
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int ret = -ENOENT;
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int ret;
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WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
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@ -1267,16 +1309,18 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key)
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b = __select_bucket(htab, hash);
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head = &b->head;
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flags = htab_lock_bucket(htab, b);
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ret = htab_lock_bucket(htab, b, hash, &flags);
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if (ret)
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return ret;
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l = lookup_elem_raw(head, hash, key, key_size);
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if (l) {
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if (l)
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hlist_nulls_del_rcu(&l->hash_node);
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ret = 0;
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}
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else
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ret = -ENOENT;
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, hash, flags);
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if (l)
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bpf_lru_push_free(&htab->lru, &l->lru_node);
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return ret;
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@ -1302,6 +1346,7 @@ static void delete_all_elements(struct bpf_htab *htab)
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static void htab_map_free(struct bpf_map *map)
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{
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struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
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int i;
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/* bpf_free_used_maps() or close(map_fd) will trigger this map_free callback.
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* bpf_free_used_maps() is called after bpf prog is no longer executing.
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@ -1320,6 +1365,8 @@ static void htab_map_free(struct bpf_map *map)
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free_percpu(htab->extra_elems);
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bpf_map_area_free(htab->buckets);
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lockdep_unregister_key(&htab->lockdep_key);
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for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
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free_percpu(htab->map_locked[i]);
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kfree(htab);
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}
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@ -1423,8 +1470,11 @@ again_nocopy:
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b = &htab->buckets[batch];
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head = &b->head;
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/* do not grab the lock unless need it (bucket_cnt > 0). */
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if (locked)
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flags = htab_lock_bucket(htab, b);
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if (locked) {
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ret = htab_lock_bucket(htab, b, batch, &flags);
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if (ret)
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goto next_batch;
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}
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bucket_cnt = 0;
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hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)
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@ -1441,7 +1491,7 @@ again_nocopy:
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/* Note that since bucket_cnt > 0 here, it is implicit
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* that the locked was grabbed, so release it.
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*/
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, batch, flags);
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rcu_read_unlock();
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bpf_enable_instrumentation();
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goto after_loop;
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@ -1452,7 +1502,7 @@ again_nocopy:
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/* Note that since bucket_cnt > 0 here, it is implicit
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* that the locked was grabbed, so release it.
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*/
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, batch, flags);
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rcu_read_unlock();
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bpf_enable_instrumentation();
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kvfree(keys);
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@ -1505,7 +1555,7 @@ again_nocopy:
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dst_val += value_size;
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}
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htab_unlock_bucket(htab, b, flags);
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htab_unlock_bucket(htab, b, batch, flags);
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locked = false;
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while (node_to_free) {
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