netdev - Re: [PATCH] net: add POLLPRI to sock_def

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Message-Id: <20110106.105500.71107144.davem@davemloft.net>
Date:	Thu, 06 Jan 2011 10:55:00 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	leonardo.lists@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net: add POLLPRI to sock_def_readable()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 06 Jan 2011 18:44:57 +0100

> Leonardo Chiquitto found poll() could block forever on tcp sockets and
> Urgent data was received, if the event flag only contains POLLPRI.
> 
> He did a bisection and found commit 4938d7e0233 (poll: avoid extra
> wakeups in select/poll) was the source of the problem.
> 
> Problem is TCP sockets use standard sock_def_readable() function for
> their sk_data_ready() handler, and sock_def_readable() doesnt signal
> POLLPRI.
> 
> Only TCP is affected by the problem. Adding POLLPRI to the list of flags
> might trigger unnecessary schedules, but URGENT handling is such a
> seldom used feature this seems a good compromise.
> 
> Thanks a lot to Leonardo for providing the bisection result and a test
> program as well.
> 
> Reference : http://www.spinics.net/lists/netdev/msg151793.html
> 
> Reported-and-bisected-by: Leonardo Chiquitto <leonardo.lists@...il.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> Tested-by: Eric Dumazet <eric.dumazet@...il.com>

Applied, thanks everyone.
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