Re: generic/068 crash on 5.18-rc2?

Darrick J. Wong
2022-05-03T17:25:41Z

On Tue, May 03, 2022 at 05:31:01AM +0100, Matthew Wilcox wrote:
> On Mon, May 02, 2022 at 08:25:34PM -0700, Darrick J. Wong wrote:
> > On Mon, May 02, 2022 at 08:20:00AM -0400, Brian Foster wrote:
> > > On Sat, Apr 30, 2022 at 10:40:31PM +0100, Matthew Wilcox wrote:
> > > > On Sat, Apr 30, 2022 at 04:44:07AM +0100, Matthew Wilcox wrote:
> > > > > (I do not love this, have not even compiled it; it's late. We may be
> > > > > better off just storing next_folio inside the folio_iter).
> > > >
> > > > Does anyone have a preference for fixing this between Option A:
> > > >
> > >
> > > After seeing the trace in my previous mail and several thousand
> > > successful iterations of the test hack, I had reworked it into this
> > > (which survived weekend testing until it ran into some other XFS problem
> > > that looks unrelated):
> > >
> > > diff --git a/include/linux/bio.h b/include/linux/bio.h
> > > index 278cc81cc1e7..aa820e09978e 100644
> > > --- a/include/linux/bio.h
> > > +++ b/include/linux/bio.h
> > > @@ -269,6 +269,7 @@ struct folio_iter {
> > > size_t offset;
> > > size_t length;
> > > /* private: for use by the iterator */
> > > + struct folio *_next;
> > > size_t _seg_count;
> > > int _i;
> > > };
> > > @@ -279,6 +280,7 @@ static inline void bio_first_folio(struct folio_iter *fi, struct bio *bio,
> > > struct bio_vec *bvec = bio_first_bvec_all(bio) + i;
> > >
> > > fi->folio = page_folio(bvec->bv_page);
> > > + fi->_next = folio_next(fi->folio);
> > > fi->offset = bvec->bv_offset +
> > > PAGE_SIZE * (bvec->bv_page - &fi->folio->page);
> > > fi->_seg_count = bvec->bv_len;
> > > @@ -290,13 +292,15 @@ static inline void bio_next_folio(struct folio_iter *fi, struct bio *bio)
> > > {
> > > fi->_seg_count -= fi->length;
> > > if (fi->_seg_count) {
> > > - fi->folio = folio_next(fi->folio);
> > > + fi->folio = fi->_next;
> > > + fi->_next = folio_next(fi->folio);
> > > fi->offset = 0;
> > > fi->length = min(folio_size(fi->folio), fi->_seg_count);
> > > } else if (fi->_i + 1 < bio->bi_vcnt) {
> > > bio_first_folio(fi, bio, fi->_i + 1);
> > > } else {
> > > fi->folio = NULL;
> > > + fi->_next = NULL;
> > > }
> > > }
> > >
> > > So FWIW, that is just to say that I find option A to be cleaner and more
> > > readable.
> >
> > Me too. I'll queue up the usual nightly tests with that patch added and
> > we'll see how that does.
>
> I've just pushed essentially that patch to my for-next tree in case
> anybody does any testing with that. I'll give it a couple of days
> before creating a folio-5.18f tag and asking Linus to pull the first two
> commits on
>
> git://git.infradead.org/users/willy/pagecache.git for-next
>
> That is, commits
>
> 1a4c97e2dd5b ("block: Do not call folio_next() on an unreferenced folio")
> 095099da208b ("mm/readahead: Fix readahead with large folios")

Hmm. Well, I added 1a4c97 to my tree last night, and it seems to have
cleared up all but two of the problems I saw with the for-next branch.

generic/388 still fails (40 minutes in) with:

WARN_ON_ONCE(atomic_read(&iop->write_bytes_pending));
VM_BUG_ON_FOLIO(i_blocks_per_folio(inode, folio) > 1 && !iop, folio);

Which I think is the same problem where the fs goes down, XFS throws an
error back to iomap_do_writepages, and it tries to discard a folio that
already had writeback running on it.

There's also the same problem I reported a few days ago in xfs/501
on a 64k-page ARM64 VM where:

run fstests xfs/501 at 2022-05-02 21:17:31
XFS: Assertion failed: IS_ALIGNED((unsigned long)lv->lv_buf, sizeof(uint64_t)), file: fs/xfs/xfs_log_cil.c, line: 430
XFS: Assertion failed: IS_ALIGNED((unsigned long)buf, sizeof(uint64_t)), file: fs/xfs/xfs_log.c, line: 137
XFS: Assertion failed: IS_ALIGNED((unsigned long)buf, sizeof(uint64_t)), file: fs/xfs/xfs_log.c, line: 137

But I think that's a new bug that came in with all the log buffer
alignment changes in the 5.19 branch.

Oh. My tree still had the "disable large folios" patch in it. I guess
the "successful" results are mostly invalid then.

--D

> (more than happy to update anything about those patches)