net: Avoid race between network down and sysfs

Signed-off-by: NStephen Hemminger <shemminger@vyatta.com>
Acked-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/net-sysfs.c

@@ -77,7 +77,9 @@ static ssize_t netdev_store(struct device *dev, struct device_attribute *attr,
 	if (endp == buf)
 		goto err;
 
-	rtnl_lock();
+	if (!rtnl_trylock())
+		return -ERESTARTSYS;
+
 	if (dev_isalive(net)) {
 		if ((ret = (*set)(net, new)) == 0)
 			ret = len;