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From: Sunil Pandey <skpgkp2@sourceware.org>
To: glibc-cvs@sourceware.org
Subject: [glibc/release/2.34/master] Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537]
Date: Wed, 28 Sep 2022 16:05:59 +0000 (GMT)	[thread overview]
Message-ID: <20220928160559.43357385782C@sourceware.org> (raw)

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ed8300c054cae4aeb0bbfa043f5fccc91a4adbf5

commit ed8300c054cae4aeb0bbfa043f5fccc91a4adbf5
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.
    
    Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
    (cherry picked from commit 49302b8fdf9103b6fc0a398678668a22fa19574c)

Diff:
---
 nptl/pthread_mutex_timedlock.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index 11ad7005d0..90cede9446 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -234,12 +234,12 @@ __pthread_mutex_clocklock_common (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;

                 reply	other threads:[~2022-09-28 16:05 UTC|newest]

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