linux-kernel - Re: [PATCH] cancel_delayed_work: use del_timer() instead of del_timer

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Date:	Fri, 27 Apr 2007 11:23:49 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Jarek Poplawski <jarkao2@...pl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	David Miller <davem@...emloft.net>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cancel_delayed_work: use del_timer() instead of del_timer_sync()

On 04/27, Jarek Poplawski wrote:
>
> According to workqueue.h:
> > /*
> >  * Kill off a pending schedule_delayed_work().  Note that the work callback
> >  * function may still be running on return from cancel_delayed_work().  Run
> >  * flush_workqueue() or cancel_work_sync() to wait on it.
> >  */
> > static inline int cancel_delayed_work(struct delayed_work *work)
> 
> So, we can do something like this:
> 
> cancel_delayed_work(dwork);
> flush_workqueue(wq);
> kfree(some_obj_used_by_dwork_func);
> 
> And this is enough to work with not rearming work.
> 
> But no more after this patch...

Yes, you are right, and so this patch is wrong.

This is even documented in the changelog, with this change cancel_delayed_work()
may return while the queueing is in progress. However, in that case we can not
rely on flush_workqueue/cancel_work_sync.

Thanks a lot!

Oleg.

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