Re: [PATCH] iomap: fix memory corruption when recording errors during writeback

[Matthew Wilcox <willy@infradead.org>]

On Thu, Sep 29, 2022 at 11:44:49AM -0700, Darrick J. Wong wrote:
> Fixes: e735c0079465 ("iomap: Convert iomap_add_to_ioend() to take a folio")
> Probably-Fixes: 598ecfbaa742 ("iomap: lift the xfs writeback code to iomap")

I think this is a misuse of Fixes.  As I understand it, Fixes: is "Here's
the commit that introduced the bug", not "This is the most recent change
after which this patch will still apply".  e735c0079465 only changed
s/page/folio/ in this line of code, so clearly didn't introduce the bug.

Any kernel containing 598ecfbaa742 has this same bug, so that should be
the Fixes: line.  As you say though, 598ecfbaa742 merely moved the code
from xfs_writepage_map().  bfce7d2e2d5e moved it from xfs_do_writepage(),
but 150d5be09ce4 introduced it.  Six years ago!  Good find.  So how about:

Fixes: 150d5be09ce4 ("xfs: remove xfs_cancel_ioend")

Also,

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  fs/iomap/buffered-io.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index ca5c62901541..77d59c159248 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1421,7 +1421,7 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
>  	if (!count)
>  		folio_end_writeback(folio);
>  done:
> -	mapping_set_error(folio->mapping, error);
> +	mapping_set_error(inode->i_mapping, error);
>  	return error;
>  }
>