[PATCH v2] xfs: remove unknown compat feature check in superblock write validation

[PATCH v2] xfs: remove unknown compat feature check in superblock write validation

[Long Li]

Compat features are new features that older kernels can safely ignore,
allowing read-write mounts without issues. The current sb write validation
implementation returns -EFSCORRUPTED for unknown compat features,
preventing filesystem write operations and contradicting the feature's
definition.

Additionally, if the mounted image is unclean, the log recovery may need
to write to the superblock. Returning an error for unknown compat features
during sb write validation can cause mount failures.

Although XFS currently does not use compat feature flags, this issue
affects current kernels' ability to mount images that may use compat
feature flags in the future.

Since superblock read validation already warns about unknown compat
features, it's unnecessary to repeat this warning during write validation.
Therefore, the relevant code in write validation is being removed.

Fixes: 9e037cb7972f ("xfs: check for unknown v5 feature bits in superblock write verifier")
Cc: <stable@vger.kernel.org> # v4.19+
Signed-off-by: Long Li <leo.lilong@huawei.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
---
V2: Collect reviewed tags and cc stable mail list.

 fs/xfs/libxfs/xfs_sb.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index d95409f3cba6..02ebcbc4882f 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -297,13 +297,6 @@ xfs_validate_sb_write(
 	 * the kernel cannot support since we checked for unsupported bits in
 	 * the read verifier, which means that memory is corrupt.
 	 */
-	if (xfs_sb_has_compat_feature(sbp, XFS_SB_FEAT_COMPAT_UNKNOWN)) {
-		xfs_warn(mp,
-"Corruption detected in superblock compatible features (0x%x)!",
-			(sbp->sb_features_compat & XFS_SB_FEAT_COMPAT_UNKNOWN));
-		return -EFSCORRUPTED;
-	}
-
 	if (!xfs_is_readonly(mp) &&
 	    xfs_sb_has_ro_compat_feature(sbp, XFS_SB_FEAT_RO_COMPAT_UNKNOWN)) {
 		xfs_alert(mp,
-- 
2.39.2

Re: [PATCH v2] xfs: remove unknown compat feature check in superblock write validation

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2] xfs: remove unknown compat feature check in superblock write validation

[Carlos Maiolino]

On Wed, 13 Nov 2024 17:17:15 +0800, Long Li wrote:
> Compat features are new features that older kernels can safely ignore,
> allowing read-write mounts without issues. The current sb write validation
> implementation returns -EFSCORRUPTED for unknown compat features,
> preventing filesystem write operations and contradicting the feature's
> definition.
> 
> Additionally, if the mounted image is unclean, the log recovery may need
> to write to the superblock. Returning an error for unknown compat features
> during sb write validation can cause mount failures.
> 
> [...]

Applied to for-next, thanks!

[1/1] xfs: remove unknown compat feature check in superblock write validation
      commit: 652f03db897ba24f9c4b269e254ccc6cc01ff1b7

Best regards,
-- 
Carlos Maiolino <cem@kernel.org>