From: Yonghong Song <y...@fb.com>
Date: Thu, 22 Feb 2018 10:10:35 -0800
> 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 <eduma...@google.com>
> Suggested-by: Eric Dumazet <eduma...@google.com>
> Signed-off-by: Yonghong Song <y...@fb.com>
Acked-by: David S. Miller <da...@davemloft.net>
