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

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Message-ID: <1358396284.3855.16.camel@cr0>
Date:	Thu, 17 Jan 2013 12:18:04 +0800
From:	Cong Wang <amwang@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org, jiri@...nulli.us
Subject: Re: [Patch net-next v4] netpoll: fix a rtnl lock assertion failure

On Wed, 2013-01-16 at 22:54 -0500, David Miller wrote:
> From: Cong Wang <amwang@...hat.com>
> Date: Thu, 17 Jan 2013 11:30:18 +0800
> 
> > On Wed, 2013-01-16 at 17:24 -0800, Eric Dumazet wrote:
> >> On Tue, 2013-01-15 at 17:34 +0800, Cong Wang wrote:
> >> >  	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.
> > 
> > Hmm, I didn't realize __dev_get_by_name() doesn't hold the device, so
> > just call dev_hold() after this?
> 
> Why not just... call dev_get_by_name()?  It doesn't hurt to over-RCU
> lock.
> 

Just that taking RCU read lock while having rtnl lock is unnecessary, no
other reason.


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