Re: [PATCH 1/6] nfs: "open code" the NFS direct write rescheduler

Andrew Morton
2006-05-19T18:43:25Z

Chuck Lever <cel@citi.umich.edu> wrote:
>
> Andrew Morton wrote:
> > Chuck Lever <cel@netapp.com> wrote:
> >> + * Prevent I/O completion while we're still rescheduling
> >> + */
> >> + dreq->outstanding++;
> >> +
> >
> > No locking.
> >
> >> dreq->count = 0;
> >> + list_for_each(pos, &dreq->rewrite_list) {
> >> + struct nfs_write_data *data =
> >> + list_entry(dreq->rewrite_list.next, struct nfs_write_data, pages);
> >> +
> >> + spin_lock(&dreq->lock);
> >> + dreq->outstanding++;
> >> + spin_unlock(&dreq->lock);
> >
> > Locking.
> >
> > Deliberate?
>
> Yes. At the top of the loop, there is no outstanding I/O, so no locking
> is needed while updating "outstanding." Inside the loop, we've
> dispatched some I/O against "dreq" so locking is needed to ensure
> outstanding is updated properly.
>

OK. Well if I asked, then others will wonder about it. A comment would
cure that problem ;)