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

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Date:	Fri, 20 Apr 2007 11:22:01 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: Fw: [PATCH -mm] workqueue: debug possible endless loop in cancel_rearming_delayed_work

On Thu, Apr 19, 2007 at 02:21:22PM +0400, Oleg Nesterov wrote:
> On 04/19, Andrew Morton wrote:
> > 
> > Begin forwarded message:
> > 
> > Date: Thu, 19 Apr 2007 08:54:04 +0200
> > From: Jarek Poplawski <jarkao2@...pl>
> > To: linux-kernel@...r.kernel.org
> > Cc: Ingo Molnar <mingo@...e.hu>
> > Subject: [PATCH -mm] workqueue: debug possible endless loop in cancel_rearming_delayed_work

At first I didn't spotted your thread is "independent" and
from your second message it seems you didn't receive all, you
expected. I wonder, if there is a need and possibility to add
somewhere (I would prefer Linus' tree git's http frontend)
addresses of developers (but not maintainers), who are
interested in CC-ing about some files' patches?. 

...
> Yes. It would be better to use cancel_work_sync() instead of flush_workqueue()
> to make this less possible (because cancel_work_sync() doesn't need to wait for
> the whole ->worklist), but we can't.
> 
> > Maybe this patch could check, if I'm not dreaming...
> 
> Also: cancel_rearming_delayed_work() will hang if it (or cancel_delayed_work())
> was already called.
> 
> I had some ideas how to make this interface reliable, but I can't see how to do
> this without uglification of the current code.

For some time I thought about using a flag (isn't there
one available after NOAUTOREL?), e.g. WORK_STRUCT_CANCEL,
as a sign:

- for a workqueue code: that the work shouldn't be queued,
nor executed, if possiblei, at first possible check.

- for a work function: to stop execution as soon as possible,
even without completing the usual job, at first possible check.

There would be a question, whether the flag should be changed
under a lock for exact synchronisation.

Cheers,
Jarek P.

PS: I hope there is no reason against going with this to lkml
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