linux-kernel - [140/272] net: add POLLPRI to sock_def

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Message-Id: <20110216001439.049568009@clark.kroah.org>
Date:	Tue, 15 Feb 2011 16:13:17 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [140/272] net: add POLLPRI to sock_def_readable()

2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Eric Dumazet <eric.dumazet@...il.com>

[ Upstream commit 2c6607c611cb7bf0a6750bcea34a258144e302c5 ]

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 net/core/sock.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1907,7 +1907,7 @@ static void sock_def_readable(struct soc
 	rcu_read_lock();
 	wq = rcu_dereference(sk->sk_wq);
 	if (wq_has_sleeper(wq))
-		wake_up_interruptible_sync_poll(&wq->wait, POLLIN |
+		wake_up_interruptible_sync_poll(&wq->wait, POLLIN | POLLPRI |
 						POLLRDNORM | POLLRDBAND);
 	sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
 	rcu_read_unlock();

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