netdev - Re: [Patch net-next v4] netpoll: fix a rtnl lock assertion failure

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Message-ID: <1358385885.32167.21.camel@edumazet-glaptop>
Date:	Wed, 16 Jan 2013 17:24:45 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <amwang@...hat.com>
Cc:	netdev@...r.kernel.org, Jiri Pirko <jiri@...nulli.us>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [Patch net-next v4] netpoll: fix a rtnl lock assertion failure

On Tue, 2013-01-15 at 17:34 +0800, Cong Wang wrote:
> From: Cong Wang <amwang@...hat.com>
> 
> v4: hold rtnl lock for the whole netpoll_setup()
> v3: remove the comment
> v2: use RCU read lock
> 
> 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
> 
> In case of other races, hold rtnl lock for the entire netpoll_setup() function.
> 
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Cc: Jiri Pirko <jiri@...nulli.us>
> Cc: David S. Miller <davem@...emloft.net>
> Signed-off-by: Cong Wang <amwang@...hat.com>
> ---
> diff --git a/net/core/netpoll.c b/net/core/netpoll.c

...

>  	if (np->dev_name)
> -		ndev = dev_get_by_name(&init_net, np->dev_name);
> +		ndev = __dev_get_by_name(&init_net, np->dev_name);

This change brings interesting bugs.

All the "goto put;" are basically wrong, and the section waiting for the
carrier and releasing/getting rtnl is buggy.

Please revert this part.


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