From: Alexei Starovoitov ast@kernel.org
[ Upstream commit 59f2f841179aa6a0899cb9cf53659149a35749b7 ]
syzbot reported the following lock sequence: cpu 2: grabs timer_base lock spins on bpf_lpm lock
cpu 1: grab rcu krcp lock spins on timer_base lock
cpu 0: grab bpf_lpm lock spins on rcu krcp lock
bpf_lpm lock can be the same. timer_base lock can also be the same due to timer migration. but rcu krcp lock is always per-cpu, so it cannot be the same lock. Hence it's a false positive. To avoid lockdep complaining move kfree_rcu() after spin_unlock.
Reported-by: syzbot+1fa663a2100308ab6eab@syzkaller.appspotmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/bpf/20240329171439.37813-1-alexei.starovoitov@gmail.... Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/lpm_trie.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c index 050fe1ebf0f7d..d0febf07051ed 100644 --- a/kernel/bpf/lpm_trie.c +++ b/kernel/bpf/lpm_trie.c @@ -308,6 +308,7 @@ static long trie_update_elem(struct bpf_map *map, { struct lpm_trie *trie = container_of(map, struct lpm_trie, map); struct lpm_trie_node *node, *im_node = NULL, *new_node = NULL; + struct lpm_trie_node *free_node = NULL; struct lpm_trie_node __rcu **slot; struct bpf_lpm_trie_key_u8 *key = _key; unsigned long irq_flags; @@ -382,7 +383,7 @@ static long trie_update_elem(struct bpf_map *map, trie->n_entries--;
rcu_assign_pointer(*slot, new_node); - kfree_rcu(node, rcu); + free_node = node;
goto out; } @@ -429,6 +430,7 @@ static long trie_update_elem(struct bpf_map *map, }
spin_unlock_irqrestore(&trie->lock, irq_flags); + kfree_rcu(free_node, rcu);
return ret; } @@ -437,6 +439,7 @@ static long trie_update_elem(struct bpf_map *map, static long trie_delete_elem(struct bpf_map *map, void *_key) { struct lpm_trie *trie = container_of(map, struct lpm_trie, map); + struct lpm_trie_node *free_node = NULL, *free_parent = NULL; struct bpf_lpm_trie_key_u8 *key = _key; struct lpm_trie_node __rcu **trim, **trim2; struct lpm_trie_node *node, *parent; @@ -506,8 +509,8 @@ static long trie_delete_elem(struct bpf_map *map, void *_key) else rcu_assign_pointer( *trim2, rcu_access_pointer(parent->child[0])); - kfree_rcu(parent, rcu); - kfree_rcu(node, rcu); + free_parent = parent; + free_node = node; goto out; }
@@ -521,10 +524,12 @@ static long trie_delete_elem(struct bpf_map *map, void *_key) rcu_assign_pointer(*trim, rcu_access_pointer(node->child[1])); else RCU_INIT_POINTER(*trim, NULL); - kfree_rcu(node, rcu); + free_node = node;
out: spin_unlock_irqrestore(&trie->lock, irq_flags); + kfree_rcu(free_parent, rcu); + kfree_rcu(free_node, rcu);
return ret; }