Re: [PATCH] iomap: Move page_done callback under the folio lock

Andreas Gruenbacher
2022-12-13T20:18:15Z

On Tue, Dec 13, 2022 at 9:03 PM Darrick J. Wong <djwong@kernel.org> wrote:
> On Tue, Dec 13, 2022 at 08:48:33PM +0100, Andreas Gruenbacher wrote:
> > Hi Darrick,
> >
> > I'd like to get the following iomap change into this merge window. This
> > only affects gfs2, so I can push it as part of the gfs2 updates if you
> > don't mind, provided that I'll get your Reviewed-by confirmation.
> > Otherwise, if you'd prefer to pass this through the xfs tree, could you
> > please take it?
>
> I don't mind you pushing changes to ->page_done through the gfs2 tree,
> but don't you need to move the other callsite at the bottom of
> iomap_write_begin?

No, in the failure case in iomap_write_begin(), the folio isn't
relevant because it's not being written to.

Thanks for paying attention,
Andreas

> --D
>
> > Thanks,
> > Andreas
> >
> > --
> >
> > Move the ->page_done() call in iomap_write_end() under the folio lock.
> > This closes a race between journaled data writes and the shrinker in
> > gfs2. What's happening is that gfs2_iomap_page_done() is called after
> > the page has been unlocked, so try_to_free_buffers() can come in and
> > free the buffers while gfs2_iomap_page_done() is trying to add them to
> > the current transaction. The folio lock prevents that from happening.
> >
> > The only user of ->page_done() is gfs2, so other filesystems are not
> > affected.
> >
> > Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> > ---
> > fs/iomap/buffered-io.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index 91ee0b308e13..476c9ed1b333 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -714,12 +714,12 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
> > i_size_write(iter->inode, pos + ret);
> > iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
> > }
> > + if (page_ops && page_ops->page_done)
> > + page_ops->page_done(iter->inode, pos, ret, &folio->page);
> > folio_unlock(folio);
> >
> > if (old_size < pos)
> > pagecache_isize_extended(iter->inode, old_size, pos);
> > - if (page_ops && page_ops->page_done)
> > - page_ops->page_done(iter->inode, pos, ret, &folio->page);
> > folio_put(folio);
> >
> > if (ret < len)
> > --
> > 2.38.1
> >
>