Subject: rtmutex: Handle non enqueued waiters gracefully From: Thomas Gleixner Date: Fri, 06 Nov 2015 18:51:03 +0100 Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.4/patches-4.4.1-rt5.tar.xz Yimin debugged that in case of a PI wakeup in progress when rt_mutex_start_proxy_lock() calls task_blocks_on_rt_mutex() the latter returns -EAGAIN and in consequence the remove_waiter() call runs into a BUG_ON() because there is nothing to remove. Guard it with rt_mutex_has_waiters(). This is a quick fix which is easy to backport. The proper fix is to have a central check in remove_waiter() so we can call it unconditionally. Reported-and-debugged-by: Yimin Deng Signed-off-by: Thomas Gleixner Cc: stable-rt@vger.kernel.org --- kernel/locking/rtmutex.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1617,7 +1617,7 @@ int rt_mutex_start_proxy_lock(struct rt_ ret = 0; } - if (unlikely(ret)) + if (ret && rt_mutex_has_waiters(lock)) remove_waiter(lock, waiter); raw_spin_unlock(&lock->wait_lock);