netdev - Re: [RFC] bonding: fix workqueue re-arming races

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Date:	Wed, 1 Sep 2010 17:18:56 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Jiri Bohac <jbohac@...e.cz>
Cc:	Jay Vosburgh <fubar@...ibm.com>,
	bonding-devel@...ts.sourceforge.net, markine@...gle.com,
	chavey@...gle.com, netdev@...r.kernel.org
Subject: Re: [RFC] bonding: fix workqueue re-arming races

On Wed, Sep 01, 2010 at 03:30:56PM +0200, Jiri Bohac wrote:
> On Wed, Sep 01, 2010 at 12:23:56PM +0000, Jarek Poplawski wrote:
> > On 2010-08-31 22:54, Jay Vosburgh wrote:
> > > 	What prevents this from deadlocking such that cpu A is in
> > > bond_close, holding RTNL and in cancel_delayed_work_sync, while cpu B is
> > > in the above function, trying to acquire RTNL?
> > 
> > I guess this one isn't cancelled in bond_close, so it should be safe.
> 
> Nah, Jay was correct. Although this work item is not explicitly
> cancelled with cancel_delayed_work_sync(), it is on the same
> workqueue as work items that are being cancelled with
> cancel_delayed_work_sync(), so this can still cause a deadlock.
> Fixed in the new version of the patch by putting these on a
> separate workqueue.
> 

Maybe I miss something, but the same workqueue shouldn't matter here.
Similar things are done by other network code with the kernel-global
workqueue.

Jarek P.
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