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Pull up following revision(s) (requested by riastradh in ticket #1861): 

sys/kern/kern_rwlock.c: revision 1.68 (patch)

rwlock(9): Fix membars.

rw_downgrade must be a release operation, and rw_tryupgrade must be
an acquire operation.  membar_producer is not enough -- need to use
membar_release and membar_acquire.

Discussed on tech-kern:
https://mail-index.netbsd.org/tech-kern/2023/02/22/msg028726.html
This commit is contained in:
martin 2023-07-31 14:49:37 +00:00
parent dd81d3bc18
commit c67cd7ca05
1 changed files with 4 additions and 5 deletions
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9
sys/kern/kern_rwlock.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: kern_rwlock.c,v 1.46.6.3 2023/07/31 14:42:45 martin Exp $ */
/* $NetBSD: kern_rwlock.c,v 1.46.6.4 2023/07/31 14:49:37 martin Exp $ */
/*-
* Copyright (c) 2002, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
@ -38,7 +38,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_rwlock.c,v 1.46.6.3 2023/07/31 14:42:45 martin Exp $");
__KERNEL_RCSID(0, "$NetBSD: kern_rwlock.c,v 1.46.6.4 2023/07/31 14:49:37 martin Exp $");
#define __RWLOCK_PRIVATE
@ -592,8 +592,7 @@ rw_downgrade(krwlock_t *rw)
__USE(curthread);
#endif
membar_producer();
membar_exit();
owner = rw->rw_owner;
if ((owner & RW_HAS_WAITERS) == 0) {
/*
@ -689,7 +688,7 @@ rw_tryupgrade(krwlock_t *rw)
newown = curthread | RW_WRITE_LOCKED | (owner & ~RW_THREAD);
next = rw_cas(rw, owner, newown);
if (__predict_true(next == owner)) {
membar_producer();
membar_enter(); /* XXX membar_acquire */
break;
}
}