[PATCH] dax: fix wrong error code returned from dax_dedupe_file_range_compare()

[PATCH] dax: fix wrong error code returned from dax_dedupe_file_range_compare()

[jianyungao89]

From: Jianyun Gao <jianyungao89@gmail.com>

When dax_range_compare_iter() returns a negative error code (e.g. -EIO),
dax_dedupe_file_range_compare() incorrectly returns 'ret' which holds the
positive return value from iomap_iter() indicating more iterations remain.
This positive value leaks to the caller, where vfs_dedupe_file_range()
interprets it as success (bytes_deduped = len), causing userspace to
incorrectly believe deduplication completed.

Return 'status' instead to propagate the actual error code.

Signed-off-by: Jianyun Gao <jianyungao89@gmail.com>
---
 fs/dax.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index 6ba50142eeb2..1f6a4fbb97bd 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -2261,7 +2261,7 @@ int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
 		status = dax_range_compare_iter(&src_iter, &dst_iter,
 				min(src_iter.len, dst_iter.len), same);
 		if (status < 0)
-			return ret;
+			return status;
 		src_iter.status = dst_iter.status = status;
 	}
 	return ret;
-- 
2.34.1

Re: [PATCH] dax: fix wrong error code returned from dax_dedupe_file_range_compare()

[Jan Kara]

On Sat 10-10-26 10:10:09, jianyungao89@gmail.com wrote:
> From: Jianyun Gao <jianyungao89@gmail.com>
> 
> When dax_range_compare_iter() returns a negative error code (e.g. -EIO),
> dax_dedupe_file_range_compare() incorrectly returns 'ret' which holds the
> positive return value from iomap_iter() indicating more iterations remain.
> This positive value leaks to the caller, where vfs_dedupe_file_range()
> interprets it as success (bytes_deduped = len), causing userspace to
> incorrectly believe deduplication completed.
> 
> Return 'status' instead to propagate the actual error code.
> 
> Signed-off-by: Jianyun Gao <jianyungao89@gmail.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/dax.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 6ba50142eeb2..1f6a4fbb97bd 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -2261,7 +2261,7 @@ int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
>  		status = dax_range_compare_iter(&src_iter, &dst_iter,
>  				min(src_iter.len, dst_iter.len), same);
>  		if (status < 0)
> -			return ret;
> +			return status;
>  		src_iter.status = dst_iter.status = status;
>  	}
>  	return ret;
> -- 
> 2.34.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH] dax: fix wrong error code returned from dax_dedupe_file_range_compare()

[Markus Elfring]

…
> Return 'status' instead to propagate the actual error code.

How do you think about to add any tags (like “Fixes” and “Cc”) accordingly?

See also:
* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v7.3-rc7#n145
* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/stable-kernel-rules.rst?h=v7.3-rc7#n34


Regards,
Markus

Re: [PATCH] dax: fix wrong error code returned from dax_dedupe_file_range_compare()

[Jianyun Gao]

Hi Markus,

Thank you for the suggestion! I will add the "Fixes" and "Cc" tags in
the next version.

Best regards,
Jianyun

On Mon, Oct 12, 2026 at 9:40 PM Markus Elfring <Markus.Elfring@web.de> wrote:
>
> …
> > Return 'status' instead to propagate the actual error code.
>
> How do you think about to add any tags (like “Fixes” and “Cc”) accordingly?
>
> See also:
> * https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v7.3-rc7#n145
> * https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/stable-kernel-rules.rst?h=v7.3-rc7#n34
>
>
> Regards,
> Markus