From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 7 Sep 2017 12:38:47 +0200
Subject: locking/rtmutex: don't drop the wait_lock twice
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 4c48f931809a4d82d69d97935c8d3578e8f4697a
Patch-mainline: Queued in subsystem maintainer repository
References: SLE12 Realtime Extension

Since the futex rework, __rt_mutex_start_proxy_lock() does no longer
acquire the wait_lock so it must not drop it. Otherwise the lock is not
only unlocked twice but also the preemption counter is underflown.

It is okay to remove that line because this function does not disable
interrupts nor does it acquire the ->wait_lock. The caller does this so it is
wrong do it here (after the futex rework).

Cc: rt-stable@vger.kernel.org #v4.9.18-rt14+
Reported-by: Gusenleitner Klaus <gus@keba.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 kernel/locking/rtmutex.c |    1 -
 1 file changed, 1 deletion(-)

--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -2325,7 +2325,6 @@ int __rt_mutex_start_proxy_lock(struct r
 	raw_spin_lock(&task->pi_lock);
 	if (task->pi_blocked_on) {
 		raw_spin_unlock(&task->pi_lock);
-		raw_spin_unlock_irq(&lock->wait_lock);
 		return -EAGAIN;
 	}
 	task->pi_blocked_on = PI_REQUEUE_INPROGRESS;