Re: [PATCH 05/10] writeback: support > 1 flusher thread per bdi

[Artem Bityutskiy]

Jamie Lokier wrote:
> Artem Bityutskiy wrote:
> > Jens Axboe wrote:
> > > +static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work 
> > > *work)
> > > +{
> > > +	if (work) {
> > > +		work->seen = bdi->wb_mask;
> > > +		BUG_ON(!work->seen);
> > > +		atomic_set(&work->pending, bdi->wb_cnt);
> > > +		BUG_ON(!bdi->wb_cnt);
> > > +
> > > +		/*
> > > +		 * Make sure stores are seen before it appears on the list
> > > +		 */
> > > +		smp_mb();
> > > +
> > > +		spin_lock(&bdi->wb_lock);
> > > +		list_add_tail_rcu(&work->list, &bdi->work_list);
> > > +		spin_unlock(&bdi->wb_lock);
> > > +	}
> > Doesn't spin_lock() include an implicit memory barrier?
> > After &bdi->wb_lock is acquired, it is guaranteed that all
> > memory operations are finished.
>
> I'm pretty sure spin_lock() is an "acquire" barrier, which just guarantees
> loads/stores after the spin_lock() are done after taking the lock.
>
> It doesn't guarantee anything about loads/stores before the spin_lock().

Right, but comment says memops should be flushed before the
list is changed.

--
Best Regards,
Artem Bityutskiy (ÐÑÑÑÐ ÐÐÑÑÑÐÐÐ)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/