Re: [PATCH 5/8] NFSD: reduce locking in nfsd_lookup()

["NeilBrown" <neilb@suse.de>]

On Thu, 07 Jul 2022, Chuck Lever III wrote:
> > +		/* We want to keep the directory locked until we've had a chance
> > +		 * to acquire a delegation if appropriate, so request that
> > +		 * nfsd_lookup() hold on to the lock.
> > 		 */
> > 		status = nfsd_lookup(rqstp, current_fh,
> > -				     open->op_fname, open->op_fnamelen, *resfh);
> > +				     open->op_fname, open->op_fnamelen, *resfh,
> > +				     true);
> > +		if (!status) {
> > +			/* NFSv4 protocol requires change attributes even though
> > +			 * no change happened.
> > +			 */
> > +			fh_fill_pre_attrs(current_fh);
> > +			fh_fill_post_attrs(current_fh);
> 
> If this is really correct, the comment should also state that
> no concurrent changes to the parent are possible during
> the lookup, and thus the pre and post attributes are expected
> to be the same always.

The earlier comment notes that nfsd_lookup() is called in a way in which
it takes and keeps the lock - that should imply that no other changes
can happen.  But with such insane looking code, it doesn't hurt to be
extra explicit.

> 
> Otherwise, this code paragraph looks just a little insane ;-)
> 
:-)

Thanks,
NeilBrown