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Subject: rtmutex: Handle non enqueued waiters gracefully
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 06 Nov 2015 18:51:03 +0100
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 <yimin11.deng@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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
@@ -1729,7 +1729,7 @@ int __rt_mutex_start_proxy_lock(struct r
ret = 0;
}
- if (unlikely(ret))
+ if (ret && rt_mutex_has_waiters(lock))
remove_waiter(lock, waiter);
debug_rt_mutex_print_deadlock(waiter);
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