Commit 6ce47fd9 authored May 13, 2015 by Thomas Gleixner

rtmutex: Warn if trylock is called from hard/softirq context



rt_mutex_trylock() must be called from thread context. It can be
called from atomic regions (preemption or interrupts disabled), but
not from hard/softirq/nmi context. Add a warning to alert abusers.

The reasons for this are:

    1) There is a potential deadlock in the slowpath

    2) Another cpu which blocks on the rtmutex will boost the task
       which allegedly locked the rtmutex, but that cannot work
       because the hard/softirq context borrows the task context.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>

parent a22e5f57

kernel/locking/rtmutex.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -1441,10 +1441,17 @@ EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
		*
		* @lock: the rt_mutex to be locked
		*
		* This function can only be called in thread context. It's safe to
		* call it from atomic regions, but not from hard interrupt or soft
		* interrupt context.
		*
		* Returns 1 on success and 0 on contention
		*/
		int __sched rt_mutex_trylock(struct rt_mutex *lock)
		{
		if (WARN_ON(in_irq() \|\| in_nmi() \|\| in_serving_softirq()))
		return 0;

		return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
		}
		EXPORT_SYMBOL_GPL(rt_mutex_trylock);

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