linux-kernel - [tip: locking/core] locking/mutex: Use try

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Date:   Thu, 08 Jul 2021 08:42:35 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>,
        Yanfei Xu <yanfei.xu@...driver.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/core] locking/mutex: Use try_cmpxchg()

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     ab4e4d9f79b2c95ef268985d2a9625a03a73c49a
Gitweb:        https://git.kernel.org/tip/ab4e4d9f79b2c95ef268985d2a9625a03a73c49a
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Wed, 30 Jun 2021 17:35:17 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 07 Jul 2021 13:53:24 +02:00

locking/mutex: Use try_cmpxchg()

For simpler and better code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Waiman Long <longman@...hat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@...driver.com>
Link: https://lore.kernel.org/r/20210630154114.834438545@infradead.org
---
 kernel/locking/mutex.c | 27 ++++++---------------------
 1 file changed, 6 insertions(+), 21 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index cb6b112..cab7163 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -100,7 +100,7 @@ static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
 
 	owner = atomic_long_read(&lock->owner);
 	for (;;) { /* must loop, can race against a flag */
-		unsigned long old, flags = __owner_flags(owner);
+		unsigned long flags = __owner_flags(owner);
 		unsigned long task = owner & ~MUTEX_FLAGS;
 
 		if (task) {
@@ -124,11 +124,8 @@ static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
 		 */
 		flags &= ~MUTEX_FLAG_HANDOFF;
 
-		old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
-		if (old == owner)
+		if (atomic_long_try_cmpxchg_acquire(&lock->owner, &owner, curr | flags))
 			return NULL;
-
-		owner = old;
 	}
 
 	return __owner_task(owner);
@@ -168,10 +165,7 @@ static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
 {
 	unsigned long curr = (unsigned long)current;
 
-	if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
-		return true;
-
-	return false;
+	return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
 }
 #endif
 
@@ -216,7 +210,7 @@ static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
 	unsigned long owner = atomic_long_read(&lock->owner);
 
 	for (;;) {
-		unsigned long old, new;
+		unsigned long new;
 
 #ifdef CONFIG_DEBUG_MUTEXES
 		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
@@ -228,11 +222,8 @@ static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
 		if (task)
 			new |= MUTEX_FLAG_PICKUP;
 
-		old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
-		if (old == owner)
+		if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, new))
 			break;
-
-		owner = old;
 	}
 }
 
@@ -1229,8 +1220,6 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 	 */
 	owner = atomic_long_read(&lock->owner);
 	for (;;) {
-		unsigned long old;
-
 #ifdef CONFIG_DEBUG_MUTEXES
 		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
 		DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
@@ -1239,16 +1228,12 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 		if (owner & MUTEX_FLAG_HANDOFF)
 			break;
 
-		old = atomic_long_cmpxchg_release(&lock->owner, owner,
-						  __owner_flags(owner));
-		if (old == owner) {
+		if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, __owner_flags(owner))) {
 			if (owner & MUTEX_FLAG_WAITERS)
 				break;
 
 			return;
 		}
-
-		owner = old;
 	}
 
 	spin_lock(&lock->wait_lock);