Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking fix from Thomas Gleixner:
"A fix for a state leak which was introduced in the recent rework of
futex/rtmutex interaction"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
futex,rt_mutex: Fix rt_mutex_cleanup_proxy_lock()

kernel/locking/rtmutex.c

···
 	int ret;
 
 	raw_spin_lock_irq(&lock->wait_lock);
-
-	set_current_state(TASK_INTERRUPTIBLE);
-
 	/* sleep on the mutex */
+	set_current_state(TASK_INTERRUPTIBLE);
 	ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
-
+	/*
+	 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
+	 * have to fix that up.
+	 */
+	fixup_rt_mutex_waiters(lock);
 	raw_spin_unlock_irq(&lock->wait_lock);
 
 	return ret;
···
 
 	raw_spin_lock_irq(&lock->wait_lock);
 	/*
+	 * Do an unconditional try-lock, this deals with the lock stealing
+	 * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
+	 * sets a NULL owner.
+	 *
+	 * We're not interested in the return value, because the subsequent
+	 * test on rt_mutex_owner() will infer that. If the trylock succeeded,
+	 * we will own the lock and it will have removed the waiter. If we
+	 * failed the trylock, we're still not owner and we need to remove
+	 * ourselves.
+	 */
+	try_to_take_rt_mutex(lock, current, waiter);
+	/*
 	 * Unless we're the owner; we're still enqueued on the wait_list.
 	 * So check if we became owner, if not, take us off the wait_list.
 	 */
 	if (rt_mutex_owner(lock) != current) {
 		remove_waiter(lock, waiter);
-		fixup_rt_mutex_waiters(lock);
 		cleanup = true;
 	}
-
 	/*
 	 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
 	 * have to fix that up.