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

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

On Sat, Nov 09, 2024 at 08:21:24AM -0800, Darrick J. Wong wrote:
> On Sat, Nov 09, 2024 at 03:38:55PM +0800, Long Li wrote:
> > 
> > Friendly Ping ...
> 
> Sorry about that, I missed this one.
> 
> > 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.
> > > 
> 
> You might want to add this so it actually gets backported:
> 
> Cc: <stable@vger.kernel.org> # v4.19
> 

Thanks for your review, indeed, it should backport to v4.19+.

> > > Fixes: 9e037cb7972f ("xfs: check for unknown v5 feature bits in superblock write verifier")
> > > Signed-off-by: Long Li <leo.lilong@huawei.com>
> 
> Makes sense, so
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> 
> --D
> 
> > > ---
> > >  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
> > > 
> > 
>