From: Nicolas Thery <nth@dragonflybsd.org>
Date: Wed, 4 Jun 2008 04:34:54 +0000 (+0000)
Subject: Fix bugs in spin_trylock_wr():
X-Git-Tag: v2.0.1~473
X-Git-Url: https://gitweb.dragonflybsd.org/dragonfly.git/commitdiff_plain/74af985ee0ab2383594c810f54fc07da4f1e1062

Fix bugs in spin_trylock_wr():

	- globaldata.gd_spinlock_wr was not decremented back on failure;

	- incorrect comparison in loop trying to clear cached shared bits (loop
	  must fail if spinlock is still held for read by another cpu).

Reviewed-by: dillon@
---

diff --git a/sys/kern/kern_spinlock.c b/sys/kern/kern_spinlock.c
index 322f3850b2..02829a6daa 100644
--- a/sys/kern/kern_spinlock.c
+++ b/sys/kern/kern_spinlock.c
@@ -29,7 +29,7 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- * $DragonFly: src/sys/kern/kern_spinlock.c,v 1.14 2008/05/24 12:52:49 sephe Exp $
+ * $DragonFly: src/sys/kern/kern_spinlock.c,v 1.15 2008/06/04 04:34:54 nth Exp $
  */
 
 #include <sys/param.h>
@@ -125,7 +125,7 @@ exponential_init(struct exponential_backoff *bo, struct spinlock *mtx)
  * we couldn't clear (and also clear our exclusive bit).
  */
 int
-spin_trylock_wr_contested(struct spinlock *mtx, int value)
+spin_trylock_wr_contested(globaldata_t gd, struct spinlock *mtx, int value)
 {
 	int bit;
 
@@ -133,14 +133,16 @@ spin_trylock_wr_contested(struct spinlock *mtx, int value)
 	if ((value & SPINLOCK_EXCLUSIVE) == 0) {
 		while (value) {
 			bit = bsfl(value);
-			if (globaldata_find(bit)->gd_spinlock_rd != mtx) {
+			if (globaldata_find(bit)->gd_spinlock_rd == mtx) {
 				atomic_swap_int(&mtx->lock, value);
+				--gd->gd_spinlocks_wr;
 				return (FALSE);
 			}
 			value &= ~(1 << bit);
 		}
 		return (TRUE);
 	}
+	--gd->gd_spinlocks_wr;
 	return (FALSE);
 }
 
diff --git a/sys/sys/spinlock2.h b/sys/sys/spinlock2.h
index a2222cfd5f..b0fe767255 100644
--- a/sys/sys/spinlock2.h
+++ b/sys/sys/spinlock2.h
@@ -29,7 +29,7 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- * $DragonFly: src/sys/sys/spinlock2.h,v 1.11 2006/06/01 19:02:39 dillon Exp $
+ * $DragonFly: src/sys/sys/spinlock2.h,v 1.12 2008/06/04 04:34:54 nth Exp $
  */
 
 #ifndef _SYS_SPINLOCK2_H_
@@ -67,7 +67,8 @@
 
 #ifdef SMP
 
-extern int spin_trylock_wr_contested(struct spinlock *mtx, int value);
+extern int spin_trylock_wr_contested(globaldata_t gd, struct spinlock *mtx,
+    int value);
 extern void spin_lock_wr_contested(struct spinlock *mtx, int value);
 extern void spin_lock_rd_contested(struct spinlock *mtx);
 
@@ -88,7 +89,7 @@ spin_trylock_wr(struct spinlock *mtx)
 
 	++gd->gd_spinlocks_wr;
 	if ((value = atomic_swap_int(&mtx->lock, SPINLOCK_EXCLUSIVE)) != 0)
-		return (spin_trylock_wr_contested(mtx, value));
+		return (spin_trylock_wr_contested(gd, mtx, value));
 	return (TRUE);
 }