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

[Andrew Morton <akpm@osdl.org>]

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 ;)