sunrpc: Fix potential race conditions in rpc_sysfs_xprt_state_change()

We need to use test_and_set_bit() when changing xprt state flags to
avoid potentially getting xps->xps_nactive out of sync.
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/sysfs.c

@@ -309,25 +309,28 @@ static ssize_t rpc_sysfs_xprt_state_change(struct kobject *kobj,
 		goto release_tasks;
 	}
 	if (offline) {
-		set_bit(XPRT_OFFLINE, &xprt->state);
-		spin_lock(&xps->xps_lock);
-		xps->xps_nactive--;
-		spin_unlock(&xps->xps_lock);
+		if (!test_and_set_bit(XPRT_OFFLINE, &xprt->state)) {
+			spin_lock(&xps->xps_lock);
+			xps->xps_nactive--;
+			spin_unlock(&xps->xps_lock);
+		}
 	} else if (online) {
-		clear_bit(XPRT_OFFLINE, &xprt->state);
-		spin_lock(&xps->xps_lock);
-		xps->xps_nactive++;
-		spin_unlock(&xps->xps_lock);
+		if (test_and_clear_bit(XPRT_OFFLINE, &xprt->state)) {
+			spin_lock(&xps->xps_lock);
+			xps->xps_nactive++;
+			spin_unlock(&xps->xps_lock);
+		}
 	} else if (remove) {
 		if (test_bit(XPRT_OFFLINE, &xprt->state)) {
-			set_bit(XPRT_REMOVE, &xprt->state);
-			xprt_force_disconnect(xprt);
-			if (test_bit(XPRT_CONNECTED, &xprt->state)) {
-				if (!xprt->sending.qlen &&
-				    !xprt->pending.qlen &&
-				    !xprt->backlog.qlen &&
-				    !atomic_long_read(&xprt->queuelen))
-					rpc_xprt_switch_remove_xprt(xps, xprt);
+			if (!test_and_set_bit(XPRT_REMOVE, &xprt->state)) {
+				xprt_force_disconnect(xprt);
+				if (test_bit(XPRT_CONNECTED, &xprt->state)) {
+					if (!xprt->sending.qlen &&
+					    !xprt->pending.qlen &&
+					    !xprt->backlog.qlen &&
+					    !atomic_long_read(&xprt->queuelen))
+						rpc_xprt_switch_remove_xprt(xps, xprt);
+				}
 			}
 		} else {
 			count = -EINVAL;