[src/trunk]: src/sys/kern rwlock(9): Convert to membar_acquire/release.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/7eb29030c506
branches:  trunk
changeset: 365170:7eb29030c506
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sat Apr 09 23:46:19 2022 +0000

description:
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!

diffstat:

 sys/kern/kern_rwlock.c |  19 ++++++++++---------
 1 files changed, 10 insertions(+), 9 deletions(-)

diffs (70 lines):

diff -r a57361d0fbec -r 7eb29030c506 sys/kern/kern_rwlock.c
--- a/sys/kern/kern_rwlock.c    Sat Apr 09 23:46:10 2022 +0000
+++ b/sys/kern/kern_rwlock.c    Sat Apr 09 23:46:19 2022 +0000
@@ -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 @@
  * 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_WRITE_WANTED);
                        if (__predict_true(next == owner)) {
                                /* Got it! */
-                               RW_MEMBAR_ENTER();
+                               RW_MEMBAR_ACQUIRE();
                                break;
                        }
 
@@ -396,6 +396,7 @@
                        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 @@
         * 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_ASSERT(rw, (op != RW_READER && RW_OWNER(rw) == curthread) ||
            (op == RW_READER && RW_COUNT(rw) != 0));
 
-       RW_MEMBAR_ENTER();
+       RW_MEMBAR_ACQUIRE();
        return 1;
 }