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bpf: Allow RCU-protected lookups to happen from bh context

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XDP programs are called from a NAPI poll context, which means the RCU
reference liveness is ensured by local_bh_disable(). Add
rcu_read_lock_bh_held() as a condition to the RCU checks for map lookups so
lockdep understands that the dereferences are safe from inside *either* an
rcu_read_lock() section *or* a local_bh_disable() section. While both
bh_disabled and rcu_read_lock() provide RCU protection, they are
semantically distinct, so we need both conditions to prevent lockdep
complaints.

This change is done in preparation for removing the redundant
rcu_read_lock()s from drivers.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210624160609.292325-5-toke@redhat.com
This commit is contained in:
Toke Høiland-Jørgensen 2021-06-24 18:05:54 +02:00 committed by Daniel Borkmann
parent e74c74f9e5
commit 694cea395f
3 changed files with 21 additions and 12 deletions
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21
kernel/bpf/hashtab.c
View file

@ -596,7 +596,8 @@ static void *__htab_map_lookup_elem(struct bpf_map *map, void *key)
struct htab_elem *l;
u32 hash, key_size;
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
!rcu_read_lock_bh_held());
key_size = map->key_size;
@ -989,7 +990,8 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
/* unknown flags */
return -EINVAL;
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
!rcu_read_lock_bh_held());
key_size = map->key_size;
@ -1082,7 +1084,8 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value,
/* unknown flags */
return -EINVAL;
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
!rcu_read_lock_bh_held());
key_size = map->key_size;
@ -1148,7 +1151,8 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
/* unknown flags */
return -EINVAL;
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
!rcu_read_lock_bh_held());
key_size = map->key_size;
@ -1202,7 +1206,8 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
/* unknown flags */
return -EINVAL;
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
!rcu_read_lock_bh_held());
key_size = map->key_size;
@ -1276,7 +1281,8 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
u32 hash, key_size;
int ret;
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
!rcu_read_lock_bh_held());
key_size = map->key_size;
@ -1311,7 +1317,8 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key)
u32 hash, key_size;
int ret;
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() &&
!rcu_read_lock_bh_held());
key_size = map->key_size;

6
kernel/bpf/helpers.c
View file

@ -29,7 +29,7 @@
*/
BPF_CALL_2(bpf_map_lookup_elem, struct bpf_map *, map, void *, key)
{
WARN_ON_ONCE(!rcu_read_lock_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
return (unsigned long) map->ops->map_lookup_elem(map, key);
}
@ -45,7 +45,7 @@ const struct bpf_func_proto bpf_map_lookup_elem_proto = {
BPF_CALL_4(bpf_map_update_elem, struct bpf_map *, map, void *, key,
void *, value, u64, flags)
{
WARN_ON_ONCE(!rcu_read_lock_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
return map->ops->map_update_elem(map, key, value, flags);
}
@ -62,7 +62,7 @@ const struct bpf_func_proto bpf_map_update_elem_proto = {
BPF_CALL_2(bpf_map_delete_elem, struct bpf_map *, map, void *, key)
{
WARN_ON_ONCE(!rcu_read_lock_held());
WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
return map->ops->map_delete_elem(map, key);
}

6
kernel/bpf/lpm_trie.c
View file

@ -232,7 +232,8 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key)
/* Start walking the trie from the root node ... */
for (node = rcu_dereference(trie->root); node;) {
for (node = rcu_dereference_check(trie->root, rcu_read_lock_bh_held());
node;) {
unsigned int next_bit;
size_t matchlen;
@ -264,7 +265,8 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key)
* traverse down.
*/
next_bit = extract_bit(key->data, node->prefixlen);
node = rcu_dereference(node->child[next_bit]);
node = rcu_dereference_check(node->child[next_bit],
rcu_read_lock_bh_held());
}
if (!found)