Merge tag 'locking-urgent-2024-08-25' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking fix from Thomas Gleixner:
 "A single fix for rt_mutex.

  The deadlock detection code drops into an infinite scheduling loop
  while still holding rt_mutex::wait_lock, which rightfully triggers a
  'scheduling in atomic' warning.

  Unlock it before that"

* tag 'locking-urgent-2024-08-25' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rtmutex: Drop rt_mutex::wait_lock before scheduling

Author: torvalds

kernel/locking/rtmutex.c

@@ -1644,6 +1644,7 @@ static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
 }
 
 static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
+					     struct rt_mutex_base *lock,
 					     struct rt_mutex_waiter *w)
 {
 	/*
@@ -1656,10 +1657,10 @@ static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
 	if (build_ww_mutex() && w->ww_ctx)
 		return;
 
-	/*
-	 * Yell loudly and stop the task right here.
-	 */
+	raw_spin_unlock_irq(&lock->wait_lock);
+
 	WARN(1, "rtmutex deadlock detected\n");
+
 	while (1) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		rt_mutex_schedule();
@@ -1713,7 +1714,7 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
 	} else {
 		__set_current_state(TASK_RUNNING);
 		remove_waiter(lock, waiter);
-		rt_mutex_handle_deadlock(ret, chwalk, waiter);
+		rt_mutex_handle_deadlock(ret, chwalk, lock, waiter);
 	}
 
 	/*