rtmutex: Simplify rtmutex_slowtrylock() (88f2b4c1) · Commits · 戴 / test

Oleg noticed that rtmutex_slowtrylock() has a pointless check for rt_mutex_owner(lock) != current. To avoid calling try_to_take_rtmutex() we really want to check whether the lock has an owner at all or whether the trylock failed because the owner is NULL, but the RT_MUTEX_HAS_WAITERS bit is set. This covers the lock is owned by caller situation as well. We can actually do this check lockless. trylock is taking a chance whether we take lock->wait_lock to do the check or not. Add comments to the function while at it. Reported-by:

Oleg Nesterov <oleg@redhat.com> Signed-off-by:

Thomas Gleixner <tglx@linutronix.de> Reviewed-by:

Steven Rostedt <rostedt@goodmis.org> Reviewed-by:

Lai Jiangshan <laijs@cn.fujitsu.com>

kernel/locking/rtmutex.c

+20 −11

Original line number	Diff line number	Diff line
		@@ -960,22 +960,31 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
		/*
		* Slow path try-lock function:
		*/
		static inline int
		rt_mutex_slowtrylock(struct rt_mutex *lock)
		static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
		{
		int ret = 0;
		int ret;

		raw_spin_lock(&lock->wait_lock);
		/*
		* If the lock already has an owner we fail to get the lock.
		* This can be done without taking the @lock->wait_lock as
		* it is only being read, and this is a trylock anyway.
		*/
		if (rt_mutex_owner(lock))
		return 0;

		if (likely(rt_mutex_owner(lock) != current)) {
		/*
		* The mutex has currently no owner. Lock the wait lock and
		* try to acquire the lock.
		*/
		raw_spin_lock(&lock->wait_lock);

		ret = try_to_take_rt_mutex(lock, current, NULL);

		/*
		* try_to_take_rt_mutex() sets the lock waiters
		* bit unconditionally. Clean this up.
		* try_to_take_rt_mutex() sets the lock waiters bit
		* unconditionally. Clean this up.
		*/
		fixup_rt_mutex_waiters(lock);
		}

		raw_spin_unlock(&lock->wait_lock);

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