netdev - [NET]: Fix dev->qdisc race for NETDEV_TX

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Message-ID: <20070510094228.GG521@postel.suug.ch>
Date:	Thu, 10 May 2007 11:42:28 +0200
From:	Thomas Graf <tgraf@...g.ch>
To:	davem@...emloft.net
Cc:	netdev@...r.kernel.org
Subject: [NET]: Fix dev->qdisc race for NETDEV_TX_LOCKED case

When transmit fails with NETDEV_TX_LOCKED the skb is requeued
to dev->qdisc again. The dev->qdisc pointer is protected by
the queue lock which needs to be dropped when attempting to
transmit and acquired again before requeing. The problem is
that qdisc_restart() fetches the dev->qdisc pointer once and
stores it in the `q' variable which is invalidated when
dropping the queue_lock, therefore the variable needs to be
refreshed before requeueing.

Signed-off-by: Thomas Graf <tgraf@...g.ch>

Index: net-2.6/net/sched/sch_generic.c
===================================================================
--- net-2.6.orig/net/sched/sch_generic.c	2007-05-10 11:32:18.000000000 +0200
+++ net-2.6/net/sched/sch_generic.c	2007-05-10 11:34:37.000000000 +0200
@@ -139,6 +139,7 @@ static inline int qdisc_restart(struct n
 				}
 				if (ret == NETDEV_TX_LOCKED && nolock) {
 					spin_lock(&dev->queue_lock);
+					q = dev->qdisc;
 					goto collision;
 				}
 			}
-
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