Re: [PATCH v2] iomap: Make sure iomap_end is called after iomap_begin

[Christoph Hellwig <hch@infradead.org>]

On Thu, Jun 18, 2020 at 02:24:08PM +0200, Andreas Gruenbacher wrote:
> Make sure iomap_end is always called when iomap_begin succeeds.
> 
> Without this fix, iomap_end won't be called when a filesystem's
> iomap_begin operation returns an invalid mapping, bypassing any
> unlocking done in iomap_end.  With this fix, the unlocking would
> at least still happen.
> 
> This iomap_apply bug was found by Bob Peterson during code review.
> It's unlikely that such iomap_begin bugs will survive to affect
> users, so backporting this fix seems unnecessary.
> 
> Fixes: ae259a9c8593 ("fs: introduce iomap infrastructure")
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> ---
>  fs/iomap/apply.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/iomap/apply.c b/fs/iomap/apply.c
> index 76925b40b5fd..32daf8cb411c 100644
> --- a/fs/iomap/apply.c
> +++ b/fs/iomap/apply.c
> @@ -46,10 +46,11 @@ iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
>  	ret = ops->iomap_begin(inode, pos, length, flags, &iomap, &srcmap);
>  	if (ret)
>  		return ret;
> -	if (WARN_ON(iomap.offset > pos))
> -		return -EIO;
> -	if (WARN_ON(iomap.length == 0))
> -		return -EIO;
> +	if (WARN_ON(iomap.offset > pos) ||
> +	    WARN_ON(iomap.length == 0)) {
> +		written = -EIO;
> +		goto out;
> +	}

As said before please don't merge these for no good reason.