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List:       linux-stable-commits
Subject:    patch rt-mutex-fix-stale-return-value.patch queued to 2.6.21-stable tree
From:       chrisw () sous-sol ! org
Date:       2007-06-11 23:48:22
Message-ID: 200706112348.l5BNmM2n000714 () sous-sol ! org
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This is a note to let you know that we have just queued up the patch titled

     Subject: rt-mutex: Fix stale return value

to the 2.6.21-stable tree.  Its filename is

     rt-mutex-fix-stale-return-value.patch

A git repo of this tree can be found at 
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary


>From stable-bounces@linux.kernel.org  Fri Jun  8 03:16:12 2007
Message-Id: <20070608101735.036883282@inhelltoy.tec.linutronix.de>
Date: Fri, 08 Jun 2007 10:29:28 -0000
From: Thomas Gleixner <tglx@linutronix.de>
To: stable@kernel.org
Cc: kuznet@ms2.inr.ac.ru, mingo@elte.hu
Subject: rt-mutex: Fix stale return value

Alexey Kuznetsov found some problems in the pi-futex code. 

The major problem is a stale return value in rt_mutex_slowlock():

When the pi chain walk returns -EDEADLK, but the waiter was woken up 
during the phases where the locks were dropped, the rtmutex could be
acquired, but due to the stale return value -EDEADLK returned to the
caller.

Reset the return value in the woken up path.

Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

---
 kernel/rtmutex.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- linux-2.6.21.5.orig/kernel/rtmutex.c
+++ linux-2.6.21.5/kernel/rtmutex.c
@@ -659,9 +659,16 @@ rt_mutex_slowlock(struct rt_mutex *lock,
 			 * all over without going into schedule to try
 			 * to get the lock now:
 			 */
-			if (unlikely(!waiter.task))
+			if (unlikely(!waiter.task)) {
+				/*
+				 * Reset the return value. We might
+				 * have returned with -EDEADLK and the
+				 * owner released the lock while we
+				 * were walking the pi chain.
+				 */
+				ret = 0;
 				continue;
-
+			}
 			if (unlikely(ret))
 				break;
 		}


Patches currently in stable-queue which might be from tglx@linutronix.de are

queue-2.6.21/pi-futex-fix-exit-races-and-locking-problems.patch
queue-2.6.21/rt-mutex-fix-chain-walk-early-wakeup-bug.patch
queue-2.6.21/fix-show_mem-x86_64-sparsemem.patch
queue-2.6.21/rt-mutex-fix-stale-return-value.patch
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