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

@@ -309,18 +309,20 @@ static ssize_t rpc_sysfs_xprt_state_change(struct kobject *kobj,
 		goto release_tasks;
 	}
 	if (offline) {
-		set_bit(XPRT_OFFLINE, &xprt->state);
+		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);
+		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);
+			if (!test_and_set_bit(XPRT_REMOVE, &xprt->state)) {
 				xprt_force_disconnect(xprt);
 				if (test_bit(XPRT_CONNECTED, &xprt->state)) {
 					if (!xprt->sending.qlen &&
@@ -329,6 +331,7 @@ static ssize_t rpc_sysfs_xprt_state_change(struct kobject *kobj,
 					    !atomic_long_read(&xprt->queuelen))
 						rpc_xprt_switch_remove_xprt(xps, xprt);
 				}
+			}
 		} else {
 			count = -EINVAL;
 		}