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Subject[patch-stable 1/3] 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.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>

---
kernel/rtmutex.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
Index: linux-2.6.21/kernel/rtmutex.c
===================================================================
--- linux-2.6.21.orig/kernel/rtmutex.c 2007-06-08 11:56:10.000000000 +0200
+++ linux-2.6.21/kernel/rtmutex.c 2007-06-08 11:56:10.000000000 +0200
@@ -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;
}
--

-
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