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

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Message-ID: <20100901190037.GA3030@del.dom.local>
Date:	Wed, 1 Sep 2010 21:00:37 +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 05:37:30PM +0200, Jarek Poplawski wrote:
> On Wed, Sep 01, 2010 at 05:18:56PM +0200, Jarek Poplawski wrote:
> > 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.
> 
> Hmm... I missed your point completely and Jay was correct!

Hmm#2... Alas, after getting back my sobriety, I've to say that Jay
was wrong: the same workqueue shouldn't matter here. Similar things
are done by other network code with the kernel-global workqueue, eg.
in tg3_close(), rhine_close() etc. (cancel_work_sync instaed of
cancel_delayed_work_sync doesn't matter here).

Jarek P.
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