netdev - Re: [PATCH] net: skb_fclone_busy() needs to detect orphaned skb

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Date:	Thu, 13 Nov 2014 13:20:22 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Luis Henriques <luis.henriques@...onical.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Joseph Salisbury <joseph.salisbury@...onical.com>
Subject: Re: [PATCH] net: skb_fclone_busy() needs to detect orphaned skb

On Thu, 2014-11-13 at 19:15 +0000, Luis Henriques wrote:
> Hi Eric,
> 
> On Thu, Oct 30, 2014 at 10:32:34AM -0700, Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@...gle.com>
> > 
> > Some drivers are unable to perform TX completions in a bound time.
> > They instead call skb_orphan()
> > 
> > Problem is skb_fclone_busy() has to detect this case, otherwise
> > we block TCP retransmits and can freeze unlucky tcp sessions on
> > mostly idle hosts.
> > 
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Fixes: 1f3279ae0c13 ("tcp: avoid retransmits of TCP packets hanging in host queues")
> > ---
> >  This is a stable candidate.
> >  This problem is known to hurt users of linux-3.16 kernels used by guests kernels.
> >  David, I can provide backports if you want.
> >  Thanks !
> > 
> 
> We got a bug report[0] where a backport for 3.16 was provided.  Since
> I couldn't find the original backport post, I'm not sure who's the
> actual author.  Could you please confirm if this backport is correct?
> (I'm copying the patch below).
> 
> [0] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1390604
> 
> Cheers,
> --
> Luís
> 
> 

Sure ! I provided this patch indeed, I am 'The Google engineer'
mentioned in this bug report ;)

Signed-off-by: Eric Dumazet <edumazet@...gle.com>


Thanks !

> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 4e4932b5079b..a8794367cd20 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2082,7 +2082,8 @@ static bool skb_still_in_host_queue(const struct sock *sk,
>  	const struct sk_buff *fclone = skb + 1;
>  
>  	if (unlikely(skb->fclone == SKB_FCLONE_ORIG &&
> -		     fclone->fclone == SKB_FCLONE_CLONE)) {
> +		     fclone->fclone == SKB_FCLONE_CLONE &&
> +		     fclone->sk == sk)) {
>  		NET_INC_STATS_BH(sock_net(sk),
>  				 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
>  		return true;




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