Commit af9f0063 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Peter Zijlstra
Browse files

locking/rtmutex: Avoid unconditional slowpath for DEBUG_RT_MUTEXES 



With DEBUG_RT_MUTEXES enabled the fast-path rt_mutex_cmpxchg_acquire()
always fails and all lock operations take the slow path.

Provide a new helper inline rt_mutex_try_acquire() which maps to
rt_mutex_cmpxchg_acquire() in the non-debug case. For the debug case
it invokes rt_mutex_slowtrylock() which can acquire a non-contended
rtmutex under full debug coverage.

Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230908162254.999499-3-bigeasy@linutronix.de
parent 28bc55f6

kernel/locking/rtmutex.c

+20 −1
Original line number Diff line number Diff line
@@ -218,6 +218,11 @@ static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock, 
	return try_cmpxchg_acquire(&lock->owner, &old, new);

}



static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)

{

	return rt_mutex_cmpxchg_acquire(lock, NULL, current);

}



static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,

						     struct task_struct *old,

						     struct task_struct *new)
@@ -297,6 +302,20 @@ static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock, 


}



static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock);



static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)

{

	/*

	 * With debug enabled rt_mutex_cmpxchg trylock() will always fail.

	 *

	 * Avoid unconditionally taking the slow path by using

	 * rt_mutex_slow_trylock() which is covered by the debug code and can

	 * acquire a non-contended rtmutex.

	 */

	return rt_mutex_slowtrylock(lock);

}



static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,

						     struct task_struct *old,

						     struct task_struct *new)
@@ -1755,7 +1774,7 @@ static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock, 
static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,

					   unsigned int state)

{

	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))

	if (likely(rt_mutex_try_acquire(lock)))

		return 0;



	return rt_mutex_slowlock(lock, NULL, state);

kernel/locking/ww_rt_mutex.c

+1 −1
Original line number Diff line number Diff line
@@ -62,7 +62,7 @@ __ww_rt_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx, 
	}

	mutex_acquire_nest(&rtm->dep_map, 0, 0, nest_lock, ip);



	if (likely(rt_mutex_cmpxchg_acquire(&rtm->rtmutex, NULL, current))) {

	if (likely(rt_mutex_try_acquire(&rtm->rtmutex))) {

		if (ww_ctx)

			ww_mutex_set_context_fastpath(lock, ww_ctx);

		return 0;