netdev - Re: [PATCH net] tcp: remove empty skb from write queue in error cases

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Message-ID: <CADVnQynhZ3Vr9pC5_id4z5d3Y-RhVr5c-AapbQcVntZ1=DN9YA@mail.gmail.com>
Date:   Mon, 26 Aug 2019 13:18:23 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jason Baron <jbaron@...mai.com>,
        Vladimir Rutsky <rutsky@...gle.com>
Subject: Re: [PATCH net] tcp: remove empty skb from write queue in error cases

On Mon, Aug 26, 2019 at 12:19 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Vladimir Rutsky reported stuck TCP sessions after memory pressure
> events. Edge Trigger epoll() user would never receive an EPOLLOUT
> notification allowing them to retry a sendmsg().
>
> Jason tested the case of sk_stream_alloc_skb() returning NULL,
> but there are other paths that could lead both sendmsg() and sendpage()
> to return -1 (EAGAIN), with an empty skb queued on the write queue.
>
> This patch makes sure we remove this empty skb so that
> Jason code can detect that the queue is empty, and
> call sk->sk_write_space(sk) accordingly.
>
> Fixes: ce5ec440994b ("tcp: ensure epoll edge trigger wakeup when write queue is empty")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Jason Baron <jbaron@...mai.com>
> Reported-by: Vladimir Rutsky <rutsky@...gle.com>
> Cc: Soheil Hassas Yeganeh <soheil@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> ---

Acked-by: Neal Cardwell <ncardwell@...gle.com>

Nice detective work. :-) Thanks, Eric!

neal