Re: [RFC PATCH(Experimental) 2/4] Revert changes to workqueue.c

From: Oleg Nesterov
Date: Wed Feb 21 2007 - 09:32:28 EST

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())

but it is ok to do cancel_work_sync() unconditionally.


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