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

[PATCH] 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")
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

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

[Long Li]

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
> 

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

[Darrick J. Wong]

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

> > 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
> > 
> 

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

[Long Li]

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
> > > 
> > 
>