Index: kern_sx.c
===================================================================
RCS file: /usr/repo/src/sys/kern/kern_sx.c,v
retrieving revision 1.54
diff -u -p -r1.54 kern_sx.c
--- kern_sx.c	6 Jul 2007 13:20:44 -0000	1.54
+++ kern_sx.c	30 Sep 2007 22:11:16 -0000
@@ -217,15 +217,21 @@ _sx_try_slock(struct sx *sx, const char 
 {
 	uintptr_t x;
 
+retry:
 	x = sx->sx_lock;
 	KASSERT(x != SX_LOCK_DESTROYED,
 	    ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
-	if ((x & SX_LOCK_SHARED) && atomic_cmpset_acq_ptr(&sx->sx_lock, x,
-	    x + SX_ONE_SHARER)) {
-		LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
-		WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
-		curthread->td_locks++;
-		return (1);
+	if (x & SX_LOCK_SHARED) {
+		if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
+			LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
+			WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
+			curthread->td_locks++;
+			return (1);
+		}
+		/*
+		 * Number of sharers may have changed, retry.
+		 */
+		goto retry;
 	}
 
 	LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);