netdev - Re: [PATCH bpf-next] bpf,sockmap: fix sk->sk_forward_alloc warn_on in sk_stream_kill

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Date:   Fri, 27 May 2022 14:37:28 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Wang Yufen <wangyufen@...wei.com>
Cc:     ast@...nel.org, john.fastabend@...il.com, andrii@...nel.org,
        daniel@...earbox.net, jakub@...udflare.com, lmb@...udflare.com,
        davem@...emloft.net, kafai@...com, dsahern@...nel.org,
        kuba@...nel.org, songliubraving@...com, yhs@...com,
        kpsingh@...nel.org, netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf,sockmap: fix sk->sk_forward_alloc warn_on
 in sk_stream_kill_queues

On Tue, May 24, 2022 at 03:53:11PM +0800, Wang Yufen wrote:
> During TCP sockmap redirect pressure test, the following warning is triggered:
> WARNING: CPU: 3 PID: 2145 at net/core/stream.c:205 sk_stream_kill_queues+0xbc/0xd0
> CPU: 3 PID: 2145 Comm: iperf Kdump: loaded Tainted: G        W         5.10.0+ #9
> Call Trace:
>  inet_csk_destroy_sock+0x55/0x110
>  inet_csk_listen_stop+0xbb/0x380
>  tcp_close+0x41b/0x480
>  inet_release+0x42/0x80
>  __sock_release+0x3d/0xa0
>  sock_close+0x11/0x20
>  __fput+0x9d/0x240
>  task_work_run+0x62/0x90
>  exit_to_user_mode_prepare+0x110/0x120
>  syscall_exit_to_user_mode+0x27/0x190
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> The reason we observed is that:
> When the listener is closing, a connection may have completed the three-way
> handshake but not accepted, and the client has sent some packets. The child
> sks in accept queue release by inet_child_forget()->inet_csk_destroy_sock(),
> but psocks of child sks have not released.
> 

Hm, in this scenario, how does the child socket end up in the sockmap?
Clearly user-space does not have a chance to get an fd yet.

And, how does your patch work? Since the child sock does not even inheirt
the sock proto after clone (see the comments above tcp_bpf_clone()) at
all?

Thanks.