netdev - Re: [PATCH bpf] bpf, sockmap, udp: sk_prot needs inuse

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Date:   Tue, 13 Jul 2021 17:51:52 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jakub Sitnicki <jakub@...udflare.com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenz Bauer <lmb@...udflare.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf] bpf, sockmap, udp: sk_prot needs inuse_idx set for
 proc stats

On Tue, Jul 13, 2021 at 12:44 AM Jakub Sitnicki <jakub@...udflare.com> wrote:
>
> Proc socket stats use sk_prot->inuse_idx value to record inuse sock stats.
> We currently do not set this correctly from sockmap side. The result is
> reading sock stats '/proc/net/sockstat' gives incorrect values. The
> socket counter is incremented correctly, but because we don't set the
> counter correctly when we replace sk_prot we may omit the decrement.
>
> To get the correct inuse_idx value move the core_initcall that initializes
> the udp proto handlers to late_initcall. This way it is initialized after
> UDP has the chance to assign the inuse_idx value from the register protocol
> handler.

Interesting. What about IPv6 module? Based on my understanding, it should
always be loaded before we can trigger udp_bpf_check_v6_needs_rebuild().
If so, your patch is complete.

>
> Fixes: 5e21bb4e8125 ("bpf, test: fix NULL pointer dereference on invalid expected_attach_type")

Should be commit edc6741cc66059532ba621928e3f1b02a53a2f39
(bpf: Add sockmap hooks for UDP sockets), right?

Thanks.