CVS commit: src/sys/kern

[Taylor R Campbell]

Module Name:    src
Committed By:   riastradh
Date:           Sat Apr  9 23:46:19 UTC 2022

Modified Files:
        src/sys/kern: kern_rwlock.c

Log Message:
rwlock(9): Convert to membar_acquire/release.

Leave an XXX comment where I suspect there might be a missing membar
-- to be audited when I have more time to think!


To generate a diff of this commit:
cvs rdiff -u -r1.65 -r1.66 src/sys/kern/kern_rwlock.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.


Modified files:

Index: src/sys/kern/kern_rwlock.c
diff -u src/sys/kern/kern_rwlock.c:1.65 src/sys/kern/kern_rwlock.c:1.66
--- src/sys/kern/kern_rwlock.c:1.65	Sat Feb 22 21:24:45 2020
+++ src/sys/kern/kern_rwlock.c	Sat Apr  9 23:46:19 2022
@@ -1,4 +1,4 @@
-/*	$NetBSD: kern_rwlock.c,v 1.65 2020/02/22 21:24:45 ad Exp $	*/
+/*	$NetBSD: kern_rwlock.c,v 1.66 2022/04/09 23:46:19 riastradh Exp $	*/
 
 /*-
  * Copyright (c) 2002, 2006, 2007, 2008, 2009, 2019, 2020
@@ -45,7 +45,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_rwlock.c,v 1.65 2020/02/22 21:24:45 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_rwlock.c,v 1.66 2022/04/09 23:46:19 riastradh Exp $");
 
 #include "opt_lockdebug.h"
 
@@ -101,12 +101,12 @@ do { \
  * Memory barriers.
  */
 #ifdef __HAVE_ATOMIC_AS_MEMBAR
-#define	RW_MEMBAR_ENTER()
-#define	RW_MEMBAR_EXIT()
+#define	RW_MEMBAR_ACQUIRE()
+#define	RW_MEMBAR_RELEASE()
 #define	RW_MEMBAR_PRODUCER()
 #else
-#define	RW_MEMBAR_ENTER()		membar_enter()
-#define	RW_MEMBAR_EXIT()		membar_exit()
+#define	RW_MEMBAR_ACQUIRE()		membar_acquire()
+#define	RW_MEMBAR_RELEASE()		membar_release()
 #define	RW_MEMBAR_PRODUCER()		membar_producer()
 #endif
 
@@ -344,7 +344,7 @@ rw_vector_enter(krwlock_t *rw, const krw
 			    ~RW_WRITE_WANTED);
 			if (__predict_true(next == owner)) {
 				/* Got it! */
-				RW_MEMBAR_ENTER();
+				RW_MEMBAR_ACQUIRE();
 				break;
 			}
 
@@ -396,6 +396,7 @@ rw_vector_enter(krwlock_t *rw, const krw
 			continue;
 		}
 		next = rw_cas(rw, owner, owner | set_wait);
+		/* XXX membar? */
 		if (__predict_false(next != owner)) {
 			turnstile_exit(rw);
 			owner = next;
@@ -471,7 +472,7 @@ rw_vector_exit(krwlock_t *rw)
 	 * proceed to do direct handoff if there are waiters, and if the
 	 * lock would become unowned.
 	 */
-	RW_MEMBAR_EXIT();
+	RW_MEMBAR_RELEASE();
 	for (;;) {
 		newown = (owner - decr);
 		if ((newown & (RW_THREAD | RW_HAS_WAITERS)) == RW_HAS_WAITERS)
@@ -585,7 +586,7 @@ rw_vector_tryenter(krwlock_t *rw, const 
 	RW_ASSERT(rw, (op != RW_READER && RW_OWNER(rw) == curthread) ||
 	    (op == RW_READER && RW_COUNT(rw) != 0));
 
-	RW_MEMBAR_ENTER();
+	RW_MEMBAR_ACQUIRE();
 	return 1;
 }