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

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Message-Id: <20190827.213805.294784850249692598.davem@davemloft.net>
Date:   Tue, 27 Aug 2019 21:38:05 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, soheil@...gle.com, ncardwell@...gle.com,
        eric.dumazet@...il.com, jbaron@...mai.com, rutsky@...gle.com
Subject: Re: [PATCH net] tcp: remove empty skb from write queue in error
 cases

From: Eric Dumazet <edumazet@...gle.com>
Date: Mon, 26 Aug 2019 09:19:15 -0700

> 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>

Applied and queued up for -stable.