On 04/26, Jarek Poplawski wrote:
>
> On Wed, Apr 25, 2007 at 04:52:14PM +0400, Oleg Nesterov wrote:
> >
> > > It seems this
> > > change cannot do any harm, but anyway it could change a few
> > > things, e.g. with current version of cancel_rearming_delayed_work
> > > some flush_workqueue could be done needlessly, before the work
> > > is queued from timer.
> >
> > I don't think so... Could you clarify?
>
> With a code like:
>
> if (!cancel_delayed_work(dwork))
> flush_workqueue(wq);
>
> if cancel_ returns 0, and there is _queue_work in progress,
> flush_ will be done once, after this work is queued.
>
> After the patch, and the same situation flush_ also runs
> one time, but maybe without the work in a queue.
First, this is very unlikely event, and the behaviour is correct,
do you agree?
Even in this case, it is very unlikely that flush_cpu_workqueue()
will take cwq->lock before extremely short delayed_work_timer_fn.
Even if it does, work->func() likely will be completed when the
caller of flush_workqueue() will be woken by run_workquue() and
gets CPU.
Please also look at http://marc.info/?t=117699337200022&r=1
> > > It's not a big deal here, but if anybody
> > > did something like this without loop - it could matter.
> > >
> > > So, probably a lot of current code should be checked, before
> > > applying and I doubt the gain is worth of this. Maybe, for
> > > safety, make this with new name as an alternative and
> > > deprecate the current version?
> >
> > This change should not make any visible difference for the callers,
> > otherwise it is buggy.
>
> IMHO, there is the same visible difference,
> as between del_timer and del_timer_sync.
Jarek, please, could you be more explicite ? del_timer() and
del_timer_sync() are different in many ways. What exactly will
impact the user of cancel_delaye_work ?
Oleg.
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