On Mon, 2024-01-29 at 12:34 -0500, David Wysochanski wrote:
> On Mon, Jan 29, 2024 at 12:15 PM David Howells <dhowells@xxxxxxxxxx> wrote:
> >
> > Dave Wysochanski <dwysocha@xxxxxxxxxx> wrote:
> >
> > > - xas_lock(&xas);
> > > + xas_lock_irqsave(&xas, flags);
> > > xas_for_each(&xas, page, last) {
> >
> > You probably want to use RCU, not xas_lock(). The pages are locked and so
> > cannot be evicted from the xarray.
> >
>
> I tried RCU originally and ran into a problem because NFS can schedule
> (see comment on line 328 below)
>
> 326 xas_lock_irqsave(&xas, flags);
> 327 xas_for_each(&xas, page, last) {
> 328 /* nfs_read_add_folio() may schedule() due to pNFS
> layout and other RPCs */
> 329 xas_pause(&xas);
> 330 xas_unlock_irqrestore(&xas, flags);
> 331 err = nfs_read_add_folio(&pgio, ctx, page_folio(page));
> 332 if (err < 0) {
> 333 netfs->error = err;
> 334 goto out;
> 335 }
> 336 xas_lock_irqsave(&xas, flags);
> 337 }
> 338 xas_unlock_irqrestore(&xas, flags);
>
Looking at it more closely, I think you might want to just use
xa_for_each_start(). That will do the traversal using the rcu_read_lock
under the hood, and you should be able to block on every iteration.
--
Jeff Layton <jlayton@xxxxxxxxxx>
