netdev - Re: [PATCH] tcp: ensure epoll edge trigger wakeup when out of memory

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Message-ID: <1431917454.621.21.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sun, 17 May 2015 19:50:54 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Baron <jbaron@...mai.com>
Cc:	edumazet@...gle.com, davem@...emloft.net, netdev@...r.kernel.org,
	ncardwell@...gle.com, ycheng@...gle.com
Subject: Re: [PATCH] tcp: ensure epoll edge trigger wakeup when out of memory

On Fri, 2015-05-15 at 21:17 +0000, Jason Baron wrote:
> From: Jason Baron <jbaron@...mai.com>
> 
> If we really can't get an skb allocated, make sure that we let
> userspace know. This at least gives us a chance to re-try or abort.
> 
> Signed-off-by: Jason Baron <jbaron@...mai.com>
> ---
>  net/ipv4/tcp.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index ecccfdc..d7d85e8 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -986,6 +986,9 @@ do_error:
>  	if (copied)
>  		goto out;
>  out_err:
> +	/* make sure we wake any epoll edge trigger waiter */
> +	if (unlikely(sk->sk_write_queue == 0 && err == -EAGAIN))
> +		sk->sk_write_space(sk);
>  	return sk_stream_error(sk, flags, err);
>  }
>  
> @@ -1274,6 +1277,9 @@ do_error:
>  		goto out;
>  out_err:
>  	err = sk_stream_error(sk, flags, err);
> +	/* make sure we wake any epoll edge trigger waiter */
> +	if (unlikely(sk->sk_write_queue == 0 && err == -EAGAIN))
> +		sk->sk_write_space(sk);
>  	release_sock(sk);
>  	return err;
>  }

I wonder if we should return ENOMEM here, otherwise application has no
way to avoid to spin forever ?




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