From 77950da440c2b12c153b77ab8b4d1d00c88ca3a9 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Fri, 12 Nov 2021 11:47:42 -0800
Subject: [PATCH] Move assignment out of the CAS condition

Update

commit 49302b8fdf9103b6fc0a398678668a22fa19574c
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Nov 11 06:54:01 2021 -0800

    Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537]

    Replace boolean CAS with value CAS to avoid the extra load.

and

commit 0b82747dc48d5bf0871bdc6da8cb6eec1256355f
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Nov 11 06:31:51 2021 -0800

    Avoid extra load with CAS in __pthread_mutex_lock_full [BZ #28537]

    Replace boolean CAS with value CAS to avoid the extra load.

by moving assignment out of the CAS condition.

(cherry picked from commit 120ac6d238825452e8024e2f627da33b2508dfd3)
---
 nptl/pthread_mutex_lock.c      | 7 +++----
 nptl/pthread_mutex_timedlock.c | 7 +++----
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index eb4d8baa..a633d95e 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -299,10 +299,9 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 	     meantime.  */
 	  if ((oldval & FUTEX_WAITERS) == 0)
 	    {
-	      int val;
-	      if ((val = atomic_compare_and_exchange_val_acq
-		   (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
-		    oldval)) != oldval)
+	      int val = atomic_compare_and_exchange_val_acq
+		(&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval);
+	      if (val != oldval)
 		{
 		  oldval = val;
 		  continue;
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index c4627ef6..a76c30b7 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -269,10 +269,9 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex,
 	     meantime.  */
 	  if ((oldval & FUTEX_WAITERS) == 0)
 	    {
-	      int val;
-	      if ((val = atomic_compare_and_exchange_val_acq
-		   (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
-		    oldval)) != oldval)
+	      int val = atomic_compare_and_exchange_val_acq
+		(&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval);
+	      if (val != oldval)
 		{
 		  oldval = val;
 		  continue;
-- 
GitLab