[Patch net-next] netpoll: fix a rtnl lock assertion failure

[Cong Wang <amwang@redhat.com>]

From: Cong Wang <amwang@redhat.com>

This patch fixes the following warning:

[   72.013864] RTNL: assertion failed at net/core/dev.c (4955)
[   72.017758] Pid: 668, comm: netpoll-prep-v6 Not tainted 3.8.0-rc1+ #474
[   72.019582] Call Trace:
[   72.020295]  [<ffffffff8176653d>] netdev_master_upper_dev_get+0x35/0x58
[   72.022545]  [<ffffffff81784edd>] netpoll_setup+0x61/0x340
[   72.024846]  [<ffffffff815d837e>] store_enabled+0x82/0xc3
[   72.027466]  [<ffffffff815d7e51>] netconsole_target_attr_store+0x35/0x37
[   72.029348]  [<ffffffff811c3479>] configfs_write_file+0xe2/0x10c
[   72.030959]  [<ffffffff8115d239>] vfs_write+0xaf/0xf6
[   72.032359]  [<ffffffff81978a05>] ? sysret_check+0x22/0x5d
[   72.033824]  [<ffffffff8115d453>] sys_write+0x5c/0x84
[   72.035328]  [<ffffffff819789d9>] system_call_fastpath+0x16/0x1b

by holding the rtnl_lock. And as we just want test if the device
has any upper device, so I think netdev_has_any_upper_dev() is enough.

Cc: Jiri Pirko <jiri@resnulli.us>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>

---
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 9f05067..dd28cdd 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -1055,7 +1055,9 @@ int netpoll_setup(struct netpoll *np)
 		return -ENODEV;
 	}
 
-	if (netdev_master_upper_dev_get(ndev)) {
+	rtnl_lock();
+	if (netdev_has_any_upper_dev(ndev)) {
+		rtnl_unlock();
 		np_err(np, "%s is a slave device, aborting\n", np->dev_name);
 		err = -EBUSY;
 		goto put;
@@ -1066,7 +1068,6 @@ int netpoll_setup(struct netpoll *np)
 
 		np_info(np, "device %s not up yet, forcing it\n", np->dev_name);
 
-		rtnl_lock();
 		err = dev_open(ndev);
 		rtnl_unlock();
 
@@ -1094,7 +1095,8 @@ int netpoll_setup(struct netpoll *np)
 			np_notice(np, "carrier detect appears untrustworthy, waiting 4 seconds\n");
 			msleep(4000);
 		}
-	}
+	} else
+		rtnl_unlock();
 
 	if (!np->local_ip.ip) {
 		if (!np->ipv6) {