From: H.J. Lu <hjl.tools@gmail.com>
Date: Thu, 11 Nov 2021 14:31:51 +0000 (-0800)
Subject: Avoid extra load with CAS in __pthread_mutex_lock_full [BZ #28537]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f5a70409db67f3a5f035d9d6082d11efcc74910d;p=thirdparty%2Fglibc.git

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

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

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
(cherry picked from commit 0b82747dc48d5bf0871bdc6da8cb6eec1256355f)
---

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 319658adc4e..0fd7467b976 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -289,12 +289,12 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 	     meantime.  */
 	  if ((oldval & FUTEX_WAITERS) == 0)
 	    {
-	      if (atomic_compare_and_exchange_bool_acq (&mutex->__data.__lock,
-							oldval | FUTEX_WAITERS,
-							oldval)
-		  != 0)
+	      int val;
+	      if ((val = atomic_compare_and_exchange_val_acq
+		   (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
+		    oldval)) != oldval)
 		{
-		  oldval = mutex->__data.__lock;
+		  oldval = val;
 		  continue;
 		}
 	      oldval |= FUTEX_WAITERS;