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

["Darrick J. Wong" <djwong@kernel.org>]

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?

--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
>