Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.14 3/9] bpf: fix rcu lockdep warning for lpm_trie map_free callback | Date | Fri, 9 Mar 2018 16:19:08 -0800 |
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4.14-stable review patch. If anyone has any objections, please let me know.
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From: Yonghong Song <yhs@fb.com>
[ upstream commit 6c5f61023c5b0edb0c8a64c902fe97c6453b1852 ]
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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- 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 @@ -484,8 +484,7 @@ 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;
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