From ca37f880abe1c8e3464fd646fd8b89171d8fca0c Mon Sep 17 00:00:00 2001

From: "H.J. Lu" <hjl.tools@gmail.com>

Date: Thu, 11 Nov 2021 06:31:51 -0800

Subject: [PATCH] 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)

---

 nptl/pthread_mutex_lock.c | 10 +++++-----

 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c

index 29cc143e..60ada70d 100644

--- a/nptl/pthread_mutex_lock.c

+++ b/nptl/pthread_mutex_lock.c

@@ -292,12 +292,12 @@ __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;

-- 

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