Commit 88f2b4c1 authored by Thomas Gleixner's avatar Thomas Gleixner

rtmutex: Simplify rtmutex_slowtrylock()

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: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Reviewed-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
parent fddeca63
...@@ -960,22 +960,31 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, ...@@ -960,22 +960,31 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
/* /*
* Slow path try-lock function: * Slow path try-lock function:
*/ */
static inline int static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
rt_mutex_slowtrylock(struct rt_mutex *lock)
{ {
int ret = 0; int ret;
/*
* 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;
/*
* The mutex has currently no owner. Lock the wait lock and
* try to acquire the lock.
*/
raw_spin_lock(&lock->wait_lock); raw_spin_lock(&lock->wait_lock);
if (likely(rt_mutex_owner(lock) != current)) { ret = try_to_take_rt_mutex(lock, current, NULL);
ret = try_to_take_rt_mutex(lock, current, NULL); /*
/* * try_to_take_rt_mutex() sets the lock waiters bit
* try_to_take_rt_mutex() sets the lock waiters * unconditionally. Clean this up.
* bit unconditionally. Clean this up. */
*/ fixup_rt_mutex_waiters(lock);
fixup_rt_mutex_waiters(lock);
}
raw_spin_unlock(&lock->wait_lock); raw_spin_unlock(&lock->wait_lock);
......
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