Re: generic/068 crash on 5.18-rc2?

Darrick J. Wong
2022-05-05T02:40:28Z

On Tue, May 03, 2022 at 10:25:32AM -0700, Darrick J. Wong wrote:
> 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.

Well... with large folios turned back on and those two patches added to
the branch, *most* of the problems go away. The generic/388 problem
persists, and last night's run showed that the weird xfs_dquot leak that
I"ve occasionally seen on 5.18 with xfs/43[46] also exists in 5.17.

--D

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