linux-kernel - Re: [PATCH -mm] workqueue: debug possible endless loop in cancel_rearming_delayed

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Message-ID: <20070420071445.GA1695@ff.dom.local>
Date:	Fri, 20 Apr 2007 09:14:45 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH -mm] workqueue: debug possible endless loop in cancel_rearming_delayed_work

On Thu, Apr 19, 2007 at 01:07:11PM -0400, Chuck Ebbert wrote:
> Jarek Poplawski wrote:
> > Hi,
> > 
> > IMHO cancel_rearming_delayed_work is dangerous place:
> > 
> > - it assumes a work function always rearms (with no exception),
> > which probably isn't explained enough now (but anyway should
> > be checked in such loops);
> > 
> > - probably possible (theoretical) scenario: a few work
> > functions rearm themselves with very short, equal times;
> > before flush_workqueue ends, their timers are already
> > fired, so cancel_delayed_work has nothing to do.
> > 
> > Maybe this patch could check, if I'm not dreaming...
> > 
> > PS: of course the counter value below is a question of taste
> 
> Okay, an easy test for it: insmod netconsole ; rmmod netconsole
> 
> In 2.6.20.x it loops forever and cancel_rearming_delayed_work()
> is part of the trace...
 
Sure, but the dreaming test is more needed for the second
point - I mean - if it's theoretical only? The first scenario
is in my opinion assured logically - there was only a question,
whether it could be detected by other means - and it seems not.

Cheers,
Jarek P.
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