net: Fix bridgeing sysfs handling of rtnl_lock

Holding rtnl_lock when we are unregistering the sysfs files can
deadlock if we unconditionally take rtnl_lock in a sysfs file.  So fix
it with the now familiar patter of: rtnl_trylock and syscall_restart()

Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_sysfs_br.c

@@ -172,7 +172,8 @@ static ssize_t store_stp_state(struct device *d,
 	if (endp == buf)
 		return -EINVAL;
 
-	rtnl_lock();
+	if (!rtnl_trylock())
+		return restart_syscall();
 	br_stp_set_enabled(br, val);
 	rtnl_unlock();
 

net/bridge/br_sysfs_if.c

@@ -189,7 +189,8 @@ static ssize_t brport_store(struct kobject * kobj,
 
 	val = simple_strtoul(buf, &endp, 0);
 	if (endp != buf) {
-		rtnl_lock();
+		if (!rtnl_trylock())
+			return restart_syscall();
 		if (p->dev && p->br && brport_attr->store) {
 			spin_lock_bh(&p->br->lock);
 			ret = brport_attr->store(p, val);