From: Yonghong Song <yhs@fb.com>
Date: Thu, 22 Feb 2018 10:10:35 -0800
Subject: bpf: fix rcu lockdep warning for lpm_trie map_free callback
Patch-mainline: v4.16-rc3
Git-commit: 6c5f61023c5b0edb0c8a64c902fe97c6453b1852
References: bsc#1083647
Commit 9a3efb6b661f ("bpf: fix memory leak in lpm_trie map_free callback function")
fixed a memory leak and removed unnecessary locks in map_free callback function.
Unfortrunately, it introduced a lockdep warning. When lockdep checking is turned on,
running tools/testing/selftests/bpf/test_lpm_map will have:
[ 98.294321] =============================
[ 98.294807] WARNING: suspicious RCU usage
[ 98.295359] 4.16.0-rc2+ #193 Not tainted
[ 98.295907] -----------------------------
[ 98.296486] /home/yhs/work/bpf/kernel/bpf/lpm_trie.c:572 suspicious rcu_dereference_check() usage!
[ 98.297657]
[ 98.297657] other info that might help us debug this:
[ 98.297657]
[ 98.298663]
[ 98.298663] rcu_scheduler_active = 2, debug_locks = 1
[ 98.299536] 2 locks held by kworker/2:1/54:
[ 98.300152] #0: ((wq_completion)"events"){+.+.}, at: [<00000000196bc1f0>] process_one_work+0x157/0x5c0
[ 98.301381] #1: ((work_completion)(&map->work)){+.+.}, at: [<00000000196bc1f0>] process_one_work+0x157/0x5c0
Since actual trie tree removal happens only after no other
accesses to the tree are possible, replacing
rcu_dereference_protected(*slot, lockdep_is_held(&trie->lock))
with
rcu_dereference_protected(*slot, 1)
fixed the issue.
Fixes: 9a3efb6b661f ("bpf: fix memory leak in lpm_trie map_free callback function")
Reported-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Gary Lin <glin@suse.com>
---
kernel/bpf/lpm_trie.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -568,8 +568,7 @@ static void trie_free(struct bpf_map *ma
slot = &trie->root;
for (;;) {
- node = rcu_dereference_protected(*slot,
- lockdep_is_held(&trie->lock));
+ node = rcu_dereference_protected(*slot, 1);
if (!node)
goto out;