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From: Fangrui Song <maskray@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/maskray/relr] Avoid extra load with CAS in __pthread_mutex_lock_full [BZ #28537] Date: Fri, 19 Nov 2021 21:02:20 +0000 (GMT) [thread overview] Message-ID: <20211119210220.40C1C3857C42@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=0b82747dc48d5bf0871bdc6da8cb6eec1256355f 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. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com> Diff: --- 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 2bd41767e0..59a28cff1a 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -297,12 +297,12 @@ __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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