Re: [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK

[Peter Hurley]

On 02/20/2014 08:59 PM, Tejun Heo wrote:
> Hello,
>
> On Thu, Feb 20, 2014 at 08:44:46PM -0500, Peter Hurley wrote:
> > > +static void fw_device_workfn(struct work_struct *work)
> > > +{
> > > +	struct fw_device *device = container_of(to_delayed_work(work),
> > > +						struct fw_device, work);
> >
> > I think this needs an smp_rmb() here.
>
> The patch is equivalent transformation and the whole thing is
> guaranteed to have gone through pool->lock.  No explicit rmb
> necessary.

The spin_unlock_irq(&pool->lock) only guarantees completion of
memory operations _before_ the unlock; memory operations which occur
_after_ the unlock may be speculated before the unlock.

IOW, unlock is not a memory barrier for operations that occur after.

> > IOW, the beginning of the work function should act like a barrier in
> > the same way that queue_work_on() (et. al.) already does.
>
> workqueue already has enough barriers; otherwise, the whole kernel
> would have crumbled long time ago.

See above.

Regards,
Peter Hurley
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