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

[Chuck Lever <cel@citi.umich.edu>]

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.

--
corporate:	cel at netapp dot com
personal:	chucklever at bigfoot dot com
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