Commit 432efdbe authored Aug 15, 2024 by Roland Xu Committed by Greg Kroah-Hartman Sep 12, 2024

rtmutex: Drop rt_mutex::wait_lock before scheduling



commit d33d26036a0274b472299d7dcdaa5fb34329f91b upstream.

rt_mutex_handle_deadlock() is called with rt_mutex::wait_lock held.  In the
good case it returns with the lock held and in the deadlock case it emits a
warning and goes into an endless scheduling loop with the lock held, which
triggers the 'scheduling in atomic' warning.

Unlock rt_mutex::wait_lock in the dead lock case before issuing the warning
and dropping into the schedule for ever loop.

[ tglx: Moved unlock before the WARN(), removed the pointless comment,
  	massaged changelog, added Fixes tag ]

Fixes: 3d5c9340 ("rtmutex: Handle deadlock detection smarter")
Signed-off-by: Roland Xu <mu001999@outlook.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/ME0P300MB063599BEF0743B8FA339C2CECC802@ME0P300MB0635.AUSP300.PROD.OUTLOOK.COM


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 76b1dda1

kernel/locking/rtmutex.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -1205,6 +1205,7 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state,
		}

		static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
		struct rt_mutex *lock,
		struct rt_mutex_waiter *w)
		{
		/*
		@@ -1214,6 +1215,7 @@ static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
		if (res != -EDEADLOCK \|\| detect_deadlock)
		return;

		raw_spin_unlock_irq(&lock->wait_lock);
		/*
		* Yell lowdly and stop the task right here.
		*/
		@@ -1269,7 +1271,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
		if (unlikely(ret)) {
		__set_current_state(TASK_RUNNING);
		remove_waiter(lock, &waiter);
		rt_mutex_handle_deadlock(ret, chwalk, &waiter);
		rt_mutex_handle_deadlock(ret, chwalk, lock, &waiter);
		}

		/*