On Wed, Feb 21, 2007 at 05:30:10PM +0300, Oleg Nesterov wrote:
> On 02/21, Srivatsa Vaddagiri wrote:
> >
> > On Tue, Feb 20, 2007 at 11:09:36PM +0300, Oleg Nesterov wrote:
> > > > Which caller are you referring to here? Maybe we can decide on the
> > > > option after we see the users of flush_workqueue() in DOWN_PREPARE.
> > >
> > > mm/slab.c:cpuup_callback()
> >
> > The cancel_rearming_delayed_work, if used as it is in cpuup_callback,
> > will require that we send DOWN_PREPARE before freeze_processes().
> >
> > But ..I am wondering if we can avoid doing cancel_rearming_delayed_work
> > (and thus flush_workqueue) in CPU_DOWN_PREPARE of slab.c. Basically,
> >
> > mm/slab.c:
> >
> > CPU_DOWN_PREPARE: /* All processes frozen now */
> > cancel_delayed_work(&per_cpu(reap_work, cpu).timer);
> > del_work(&per_cpu(reap_work, cpu).work);
> > break;
> >
> >
> > At the point of CPU_DOWN_PREPARE, keventd should be frozen and hence
> > del_work() is a matter of just deleting the work from cwq->worklist.
>
> Agreed. Note that we don't need the new "del_work". It is always safe to
> use cancel_work_sync() if we know that the workqueue is frozen, it won't
> block. We can also do
>
> if (!cancel_delayed_work())
> cancel_work_sync();
>
> but it is ok to do cancel_work_sync() unconditionally.
True. But this might be a one off solution for slab. However, if someone
in the future might require to do a flush_workqueue from
CPU_DOWN_PREPARE context, we would need to find a new workaround.
So, I'll try running CPU_DOWN_PREPARE and CPU_UP_PREPARE from
a non frozen context to check if there are any potential problems.
Hopfully there shouldn't be (m)any!
>
> Oleg.
>
thanks and regards
gautham.
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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