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Date:   Tue, 15 Sep 2020 08:33:27 -0700
From:   Jakub Kicinski <>
To:     Yonghong Song <>
Cc:     <>, <>,
        Alexei Starovoitov <>,
        Daniel Borkmann <>, <>,
        Martin KaFai Lau <>
Subject: Re: [PATCH bpf-next] bpf: using rcu_read_lock for
 bpf_sk_storage_map iterator

On Mon, 14 Sep 2020 11:46:30 -0700 Yonghong Song wrote:
> Currently, we use bucket_lock when traversing bpf_sk_storage_map
> elements. Since bpf_iter programs cannot use bpf_sk_storage_get()
> and bpf_sk_storage_delete() helpers which may also grab bucket lock,
> we do not have a deadlock issue which exists for hashmap when
> using bucket_lock ([1]).
> If a bucket contains a lot of sockets, during bpf_iter traversing
> a bucket, concurrent bpf_sk_storage_{get,delete}() may experience
> some undesirable delays. Using rcu_read_lock() is a reasonable
> compromise here. Although it may lose some precision, e.g.,
> access stale sockets, but it will not hurt performance of other
> bpf programs.
> [1]
> Cc: Martin KaFai Lau <>
> Signed-off-by: Yonghong Song <>

Sparse is not happy about it. Could you add some annotations, perhaps?

include/linux/rcupdate.h:686:9: warning: context imbalance in 'bpf_sk_storage_map_seq_find_next' - unexpected unlock
include/linux/rcupdate.h:686:9: warning: context imbalance in 'bpf_sk_storage_map_seq_stop' - unexpected unlock

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