xfs: remove unknown compat feature check in superblock write validation

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: 9e037cb ("xfs: check for unknown v5 feature bits in superblock write verifier")
Cc: [email protected] # v4.19+
Signed-off-by: Long Li <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>

Author: Long Li

fs/xfs/libxfs/xfs_sb.c

@@ -326,13 +326,6 @@ 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,