[patch 03/26] rt-mutex: Fix stale return value

Greg KH
2007-07-31T04:30:51Z

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

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

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

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

--- linux-2.6.21.6.orig/kernel/rtmutex.c
+++ linux-2.6.21.6/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;
}

--