Commit 5de2055d authored by Waiman Long's avatar Waiman Long Committed by Ingo Molnar
Browse files

locking/ww_mutex: Simplify use_ww_ctx & ww_ctx handling 



The use_ww_ctx flag is passed to mutex_optimistic_spin(), but the
function doesn't use it. The frequent use of the (use_ww_ctx && ww_ctx)
combination is repetitive.

In fact, ww_ctx should not be used at all if !use_ww_ctx.  Simplify
ww_mutex code by dropping use_ww_ctx from mutex_optimistic_spin() an
clear ww_ctx if !use_ww_ctx. In this way, we can replace (use_ww_ctx &&
ww_ctx) by just (ww_ctx).

Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Link: https://lore.kernel.org/r/20210316153119.13802-2-longman@redhat.com
parent 1df27313

kernel/locking/mutex.c

+14 −11
Original line number Diff line number Diff line
@@ -626,7 +626,7 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock) 
 */

static __always_inline bool

mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,

		      const bool use_ww_ctx, struct mutex_waiter *waiter)

		      struct mutex_waiter *waiter)

{

	if (!waiter) {

		/*
@@ -702,7 +702,7 @@ mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx, 
#else

static __always_inline bool

mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,

		      const bool use_ww_ctx, struct mutex_waiter *waiter)

		      struct mutex_waiter *waiter)

{

	return false;

}
@@ -922,6 +922,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
	struct ww_mutex *ww;

	int ret;



	if (!use_ww_ctx)

		ww_ctx = NULL;



	might_sleep();



#ifdef CONFIG_DEBUG_MUTEXES
@@ -929,7 +932,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
#endif



	ww = container_of(lock, struct ww_mutex, base);

	if (use_ww_ctx && ww_ctx) {

	if (ww_ctx) {

		if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))

			return -EALREADY;
@@ -946,10 +949,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
	mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);



	if (__mutex_trylock(lock) ||

	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {

	    mutex_optimistic_spin(lock, ww_ctx, NULL)) {

		/* got the lock, yay! */

		lock_acquired(&lock->dep_map, ip);

		if (use_ww_ctx && ww_ctx)

		if (ww_ctx)

			ww_mutex_set_context_fastpath(ww, ww_ctx);

		preempt_enable();

		return 0;
@@ -960,7 +963,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
	 * After waiting to acquire the wait_lock, try again.

	 */

	if (__mutex_trylock(lock)) {

		if (use_ww_ctx && ww_ctx)

		if (ww_ctx)

			__ww_mutex_check_waiters(lock, ww_ctx);



		goto skip_wait;
@@ -1013,7 +1016,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
			goto err;

		}



		if (use_ww_ctx && ww_ctx) {

		if (ww_ctx) {

			ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);

			if (ret)

				goto err;
@@ -1026,7 +1029,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
		 * ww_mutex needs to always recheck its position since its waiter

		 * list is not FIFO ordered.

		 */

		if ((use_ww_ctx && ww_ctx) || !first) {

		if (ww_ctx || !first) {

			first = __mutex_waiter_is_first(lock, &waiter);

			if (first)

				__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
@@ -1039,7 +1042,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
		 * or we must see its unlock and acquire.

		 */

		if (__mutex_trylock(lock) ||

		    (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))

		    (first && mutex_optimistic_spin(lock, ww_ctx, &waiter)))

			break;



		spin_lock(&lock->wait_lock);
@@ -1048,7 +1051,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
acquired:

	__set_current_state(TASK_RUNNING);



	if (use_ww_ctx && ww_ctx) {

	if (ww_ctx) {

		/*

		 * Wound-Wait; we stole the lock (!first_waiter), check the

		 * waiters as anyone might want to wound us.
@@ -1068,7 +1071,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
	/* got the lock - cleanup and rejoice! */

	lock_acquired(&lock->dep_map, ip);



	if (use_ww_ctx && ww_ctx)

	if (ww_ctx)

		ww_mutex_lock_acquired(ww, ww_ctx);



	spin_unlock(&lock->wait_lock);