linux-kernel - Re: [BUG] Regression on behavior of EPOLLET

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Message-ID: <1327690506.3159.7.camel@edumazet-laptop>
Date:	Fri, 27 Jan 2012 19:55:06 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Nick Mathewson <nickm@...ehaven.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Alexey Moiseytsev <himeraster@...il.com>
Subject: Re: [BUG] Regression on behavior of EPOLLET | EPOLLIN for AF_UNIX
 sockets in 3.2

Le vendredi 27 janvier 2012 à 22:17 +0400, Glauber Costa a écrit :
> On 01/27/2012 09:53 PM, Eric Dumazet wrote:
> > Le vendredi 27 janvier 2012 à 12:05 -0500, Nick Mathewson a écrit :
> >> [1.] One line summary of the problem:
> >>
> >
> > Hi
> >
> > Probably coming from commit 0884d7aa24e15e72b3c07f7da910a13bb7df3592
> > (AF_UNIX: Fix poll blocking problem when reading from a stream socket)
> >
> > When we requeue skb because not completely eaten, we call again
> >
> > sk->sk_data_ready(sk, skb->len);
> >
> For the record, I just confirmed this to be the case.

A fix would be to change unix_poll() and not call sk_data_ready() when
skb is requeued.

if (!skb_queue_empty(&sk->sk_receive_queue))
	mask |= POLLIN | POLLRDNORM;

Might be tricky if we want to keep unix_poll() lockless, but quite
possible.

Or... not dequeue skb from sk_received_queue unless fully consumed.


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