linux-kernel - Re: [PATCH 3/6] workqueue: make cancel_rearming_delayed

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Message-ID: <20070208022051.GC17585@verge.net.au>
Date:	Thu, 8 Feb 2007 11:20:51 +0900
From:	Horms <horms@...ge.net.au>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Daniel Drake <dsd@...too.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 3/6] workqueue: make cancel_rearming_delayed_workqueue() work on idle dwork

On Wed, Feb 07, 2007 at 08:43:55PM +0300, Oleg Nesterov wrote:
> On 02/07, Oleg Nesterov wrote:
> > 
> > The following code
> > 
> > 	schedule_delayed_work(dw);
> > 	cancel_rearming_delayed_workqueue(dw);	// OK
> > 	cancel_rearming_delayed_workqueue(dw);	// HANGS!
> > 
> > still doesn't work.
> 
> I think we have another problem with delayed_works.
> 
> cancel_rearming_delayed_workqueue() doesn't garantee that the ->func() is not
> running upon return. I don't know if it is bug or not, the comment says nothing
> about that.
> 
> However, we have the callers which seem to assume the opposite, example
> 
> 	net/ipv4/ipvs/ip_vs_core.c
> 
> 		module_exit
> 		    ip_vs_cleanup
> 		        ip_vs_control_cleanup
> 		            cancel_rearming_delayed_work
> 		// done
> 
> This is unsafe. The module may be unloaded and the memory may be freed
> while defense_work_handler() is still running/preempted.
> 
> Unless I missed something, which side should be fixed?

Assuming the decision is to fix the ipvs side, is the fix
just to remove the call to cancel_rearming_delayed_work() in
ip_vs_control_cleanup() ?

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/

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