netdev - Re: [PATCH bpf v2] bpf: fix rcu lockdep warning for lpm_trie map

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Date:   Thu, 22 Feb 2018 10:18:05 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Yonghong Song <yhs@...com>, ast@...com, daniel@...earbox.net,
        edumazet@...gle.com, netdev@...r.kernel.org
Cc:     kernel-team@...com
Subject: Re: [PATCH bpf v2] bpf: fix rcu lockdep warning for lpm_trie
 map_free callback

On Thu, 2018-02-22 at 10:10 -0800, Yonghong Song wrote:
> 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:
> 

> Fixes: 9a3efb6b661f ("bpf: fix memory leak in lpm_trie map_free callback function")
> Reported-by: Eric Dumazet <edumazet@...gle.com>
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Yonghong Song <yhs@...com>
> ---
>  kernel/bpf/lpm_trie.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> v1 -> v2:
>  . fix sparse warning which is introduced by v1, suggested by Eric.
> 
> diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
> index a75e02c..b4b5b81 100644
> --- a/kernel/bpf/lpm_trie.c
> +++ b/kernel/bpf/lpm_trie.c
> @@ -569,8 +569,7 @@ static void trie_free(struct bpf_map *map)
>  		slot = &trie->root;
>  
>  		for (;;) {
> -			node = rcu_dereference_protected(*slot,
> -					lockdep_is_held(&trie->lock));
> +			node = rcu_dereference_protected(*slot, 1);
>  			if (!node)
>  				goto out;

SGTM, thanks !

Reviewed-by: Eric Dumazet <edumazet@...gle.com>