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Message-Id: <20210617212748.32456-3-toke@redhat.com>
Date: Thu, 17 Jun 2021 23:27:34 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: bpf@...r.kernel.org, netdev@...r.kernel.org
Cc: Martin KaFai Lau <kafai@...com>,
Hangbin Liu <liuhangbin@...il.com>,
Jesper Dangaard Brouer <brouer@...hat.com>,
Magnus Karlsson <magnus.karlsson@...il.com>,
"Paul E . McKenney" <paulmck@...nel.org>,
Jakub Kicinski <kuba@...nel.org>,
Toke Høiland-Jørgensen <toke@...hat.com>
Subject: [PATCH bpf-next v3 02/16] bpf: allow RCU-protected lookups to happen from bh context
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.
Acked-by: Martin KaFai Lau <kafai@...com>
Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
kernel/bpf/hashtab.c | 21 ++++++++++++++-------
kernel/bpf/helpers.c | 6 +++---
kernel/bpf/lpm_trie.c | 6 ++++--
3 files changed, 21 insertions(+), 12 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 6f6681b07364..72c58cc516a3 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -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;
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 544773970dbc..e880f6bb6f28 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -28,7 +28,7 @@
*/
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);
}
@@ -44,7 +44,7 @@ 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);
}
@@ -61,7 +61,7 @@ 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);
}
diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index 1b7b8a6f34ee..423549d2c52e 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -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)
--
2.32.0
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