Re: [Patch net-next v2] netpoll: fix a rtnl lock assertion failure

On Mon, 2013-01-14 at 11:32 +0100, Jiri Pirko wrote:

Mon, Jan 14, 2013 at 11:24:14AM CET, amwang@redhat.com wrote:

quoted

From: Cong Wang <redacted>

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

Just hold RCU read lock and call netdev_master_upper_dev_get_rcu(),
as suggested by Jiri.

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

---

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 9f05067..6d56b57 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c

@@ -1055,11 +1055,15 @@ int netpoll_setup(struct netpoll *np)

		return -ENODEV;
	}

-	if (netdev_master_upper_dev_get(ndev)) {
+	rcu_read_lock();
+	/* We permit devices with VLAN attached to */

I think that this comment might be misleading. Master upper is not set
not only for VLAN but for macvlan (and in future possibly for others) as well.	

OK, I will remove it.