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

diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index 180978cb2f7524b180863967be0391d32f47783d..21ebe7612f83a075da255e83febcd7ff26b29bb8 100644 (file)
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -659,9 +659,16 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
                         * 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;
                }