rtmutex: Plug preempt count leak in rt_mutex_futex_unlock()

mark_wakeup_next_waiter() already disables preemption, doing so again
leaves us with an unpaired preempt_disable().

Fixes: 2a1c60299406 ("rtmutex: Deboost before waking up the top waiter")
Signed-off-by: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1491379707.6538.2.camel@gmx.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 0e641eb473de3ab111e7afec3e601cf7b81b2734..b9550941690915bc23323cd772e060cda7d3a704 100644 (file)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1581,13 +1581,13 @@ bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
                return false; /* done */
        }
 
-       mark_wakeup_next_waiter(wake_q, lock);
        /*
-        * We've already deboosted, retain preempt_disabled when dropping
-        * the wait_lock to avoid inversion until the wakeup. Matched
-        * by rt_mutex_postunlock();
+        * We've already deboosted, mark_wakeup_next_waiter() will
+        * retain preempt_disabled when we drop the wait_lock, to
+        * avoid inversion prior to the wakeup.  preempt_disable()
+        * therein pairs with rt_mutex_postunlock().
         */
-       preempt_disable();
+       mark_wakeup_next_waiter(wake_q, lock);
 
        return true; /* call postunlock() */
 }