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From: Attilio Rao <attilio@FreeBSD.org>
Date: Sat, 3 Oct 2009 15:02:55 +0000 (UTC)
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Subject: svn commit: r197735 - head/sys/kern
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Author: attilio
Date: Sat Oct  3 15:02:55 2009
New Revision: 197735
URL: http://svn.freebsd.org/changeset/base/197735

Log:
  When releasing a lockmgr held in shared way we need to use a write memory
  barrier in order to avoid, on architectures which doesn't have strong
  ordered writes, CPU instructions reordering.
  
  Diagnosed by:	fabio

Modified:
  head/sys/kern/kern_lock.c

Modified: head/sys/kern/kern_lock.c
==============================================================================
--- head/sys/kern/kern_lock.c	Sat Oct  3 14:38:22 2009	(r197734)
+++ head/sys/kern/kern_lock.c	Sat Oct  3 15:02:55 2009	(r197735)
@@ -241,7 +241,7 @@ wakeupshlk(struct lock *lk, const char *
 		 * and return.
 		 */
 		if (LK_SHARERS(x) > 1) {
-			if (atomic_cmpset_ptr(&lk->lk_lock, x,
+			if (atomic_cmpset_rel_ptr(&lk->lk_lock, x,
 			    x - LK_ONE_SHARER))
 				break;
 			continue;
@@ -254,7 +254,7 @@ wakeupshlk(struct lock *lk, const char *
 		if ((x & LK_ALL_WAITERS) == 0) {
 			MPASS((x & ~LK_EXCLUSIVE_SPINNERS) ==
 			    LK_SHARERS_LOCK(1));
-			if (atomic_cmpset_ptr(&lk->lk_lock, x, LK_UNLOCKED))
+			if (atomic_cmpset_rel_ptr(&lk->lk_lock, x, LK_UNLOCKED))
 				break;
 			continue;
 		}
@@ -280,7 +280,7 @@ wakeupshlk(struct lock *lk, const char *
 			queue = SQ_SHARED_QUEUE;
 		}
 
-		if (!atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x,
+		if (!atomic_cmpset_rel_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x,
 		    v)) {
 			sleepq_release(&lk->lock_object);
 			continue;