From 07c73e384bf896225c43f65ec89cc0e0a9e03960 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Thu, 31 Mar 2022 02:39:59 +0000
Subject: [PATCH 36/49] mutex(9): Convert to membar_acquire/release.
Except for setting the waiters bit -- not sure if this is actually
required to be store-before-load/store. Seems unlikely -- surely
we'd have seen some serious bug by now if not, because membar_enter
has failed to guarantee that on x86! -- but I'm leaving it for now
until I have time to think enough about it to be sure one way or
another.
---
sys/kern/kern_mutex.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c
index e94157ba77e7..57a546c5e172 100644
--- a/sys/kern/kern_mutex.c
+++ b/sys/kern/kern_mutex.c
@@ -169,10 +169,12 @@ do { \
*/
#ifdef __HAVE_ATOMIC_AS_MEMBAR
#define MUTEX_MEMBAR_ENTER()
-#define MUTEX_MEMBAR_EXIT()
+#define MUTEX_MEMBAR_ACQUIRE()
+#define MUTEX_MEMBAR_RELEASE()
#else
#define MUTEX_MEMBAR_ENTER() membar_enter()
-#define MUTEX_MEMBAR_EXIT() membar_exit()
+#define MUTEX_MEMBAR_ACQUIRE() membar_acquire()
+#define MUTEX_MEMBAR_RELEASE() membar_release()
#endif
/*
@@ -238,7 +240,7 @@ MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
MUTEX_INHERITDEBUG(oldown, mtx->mtx_owner);
MUTEX_INHERITDEBUG(newown, oldown);
rv = MUTEX_CAS(&mtx->mtx_owner, oldown, newown);
- MUTEX_MEMBAR_ENTER();
+ MUTEX_MEMBAR_ACQUIRE();
return rv;
}
@@ -256,7 +258,7 @@ MUTEX_RELEASE(kmutex_t *mtx)
{
uintptr_t newown;
- MUTEX_MEMBAR_EXIT();
+ MUTEX_MEMBAR_RELEASE();
newown = 0;
MUTEX_INHERITDEBUG(newown, mtx->mtx_owner);
mtx->mtx_owner = newown;