rtmutex: Simplify rtmutex_slowtrylock()
upstream-commit: 88f2b4c15e
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>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Conflicts:
kernel/locking/rtmutex.c
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@ -1465,23 +1465,32 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
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/*
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* Slow path try-lock function:
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*/
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static inline int
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rt_mutex_slowtrylock(struct rt_mutex *lock)
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static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
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{
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int ret = 0;
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int ret;
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/*
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* If the lock already has an owner we fail to get the lock.
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* This can be done without taking the @lock->wait_lock as
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* it is only being read, and this is a trylock anyway.
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*/
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if (rt_mutex_owner(lock))
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return 0;
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/*
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* The mutex has currently no owner. Lock the wait lock and
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* try to acquire the lock.
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*/
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if (!raw_spin_trylock(&lock->wait_lock))
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return ret;
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return 0;
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if (likely(rt_mutex_owner(lock) != current)) {
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ret = try_to_take_rt_mutex(lock, current, NULL);
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ret = try_to_take_rt_mutex(lock, current, NULL);
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/*
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* try_to_take_rt_mutex() sets the lock waiters
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* bit unconditionally. Clean this up.
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*/
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fixup_rt_mutex_waiters(lock);
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}
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/*
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* try_to_take_rt_mutex() sets the lock waiters bit
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* unconditionally. Clean this up.
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*/
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fixup_rt_mutex_waiters(lock);
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raw_spin_unlock(&lock->wait_lock);
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