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

[Long Li <leo.lilong@huawei.com>]

Friendly Ping ...

On Mon, Oct 21, 2024 at 09:25:49AM +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.
> 
> 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")
> Signed-off-by: Long Li <leo.lilong@huawei.com>
> ---
>  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
>