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Date:   Mon, 14 Sep 2020 14:28:22 -0700
From:   Song Liu <>
To:     Yonghong Song <>
Cc:     bpf <>, Networking <>,
        Alexei Starovoitov <>,
        Daniel Borkmann <>,
        Kernel Team <>,
        Martin KaFai Lau <>
Subject: Re: [PATCH bpf-next] bpf: using rcu_read_lock for bpf_sk_storage_map iterator

On Mon, Sep 14, 2020 at 11:47 AM 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]).

The paragraph above describes why we can use bucket_lock, which is more
or less irrelevant to this change. Also, I am not sure why we refer to [1] here.

> 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

It will be great to include some performance comparison.

> 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 <>

Other than these,

Acked-by: Song Liu <>


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