linux-ext4 - Re: [PATCH v5 1/1] xfs: Fail remount with noattr2 on a v5 with v4 enabled

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Message-ID: <xwx4pyblttfkrxfq3wlorwz743oathzvjdigehgke4gsu6vona@xfftyhxmzr22>
Date: Mon, 12 May 2025 13:10:47 +0200
From: Carlos Maiolino <cem@...nel.org>
To: "Nirjhar Roy (IBM)" <nirjhar.roy.lists@...il.com>
Cc: linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org, 
	fstests@...r.kernel.org, ritesh.list@...il.com, ojaswin@...ux.ibm.com, djwong@...nel.org, 
	zlang@...nel.org, david@...morbit.com, hch@...radead.org
Subject: Re: [PATCH v5 1/1] xfs: Fail remount with noattr2 on a v5 with v4
 enabled

On Mon, May 12, 2025 at 03:27:14PM +0530, Nirjhar Roy (IBM) wrote:
> Bug: When we compile the kernel with CONFIG_XFS_SUPPORT_V4=y,
> remount with "-o remount,noattr2" on a v5 XFS does not
> fail explicitly.
> 
> Reproduction:
> mkfs.xfs -f /dev/loop0
> mount /dev/loop0 /mnt/scratch
> mount -o remount,noattr2 /dev/loop0 /mnt/scratch
> 
> However, with CONFIG_XFS_SUPPORT_V4=n, the remount
> correctly fails explicitly. This is because the way the
> following 2 functions are defined:
> 
> static inline bool xfs_has_attr2 (struct xfs_mount *mp)
> {
> 	return !IS_ENABLED(CONFIG_XFS_SUPPORT_V4) ||
> 		(mp->m_features & XFS_FEAT_ATTR2);
> }
> static inline bool xfs_has_noattr2 (const struct xfs_mount *mp)
> {
> 	return mp->m_features & XFS_FEAT_NOATTR2;
> }
> 
> xfs_has_attr2() returns true when CONFIG_XFS_SUPPORT_V4=n
> and hence, the following if condition in
> xfs_fs_validate_params() succeeds and returns -EINVAL:
> 
> /*
>  * We have not read the superblock at this point, so only the attr2
>  * mount option can set the attr2 feature by this stage.
>  */
> 
> if (xfs_has_attr2(mp) && xfs_has_noattr2(mp)) {
> 	xfs_warn(mp, "attr2 and noattr2 cannot both be specified.");
> 	return -EINVAL;
> }
> 
> With CONFIG_XFS_SUPPORT_V4=y, xfs_has_attr2() always return
> false and hence no error is returned.
> 
> Fix: Check if the existing mount has crc enabled(i.e, of
> type v5 and has attr2 enabled) and the
> remount has noattr2, if yes, return -EINVAL.
> 
> I have tested xfs/{189,539} in fstests with v4
> and v5 XFS with both CONFIG_XFS_SUPPORT_V4=y/n and
> they both behave as expected.
> 
> This patch also fixes remount from noattr2 -> attr2 (on a v4 xfs).
> 
> Related discussion in [1]
> 
> [1] https://lore.kernel.org/all/Z65o6nWxT00MaUrW@dread.disaster.area/
> 
> Signed-off-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@...il.com>
> Reviewed-by: Christoph Hellwig <hch@....de>
> ---
>  fs/xfs/xfs_super.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index b2dd0c0bf509..606a95ac816f 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -2114,6 +2114,21 @@ xfs_fs_reconfigure(
>  	if (error)
>  		return error;
> 
> +	/* attr2 -> noattr2 */
> +	if (xfs_has_noattr2(new_mp)) {
> +		if (xfs_has_crc(mp)) {
> +			xfs_warn(mp,
> +			"attr2 is always enabled for a V5 filesystem - can't be changed.");
> +			return -EINVAL;

This looks good to me now:

Reviewed-by: Carlos Maiolino <cmaiolino@...hat.com>

I still wish hch's opinion here though before merging it. Giving his was the
first RwB, I want to make sure he still keeps his RwB with the above change.


FWIW, for a next patch, there is no need to copy ext4 list for a code change
that is totally unrelated to ext4. This just generates unnecessary extra
traffic.


> +		}
> +		mp->m_features &= ~XFS_FEAT_ATTR2;
> +		mp->m_features |= XFS_FEAT_NOATTR2;
> +	} else if (xfs_has_attr2(new_mp)) {
> +		/* noattr2 -> attr2 */
> +		mp->m_features &= ~XFS_FEAT_NOATTR2;
> +		mp->m_features |= XFS_FEAT_ATTR2;
> +	}
> +
>  	/* inode32 -> inode64 */
>  	if (xfs_has_small_inums(mp) && !xfs_has_small_inums(new_mp)) {
>  		mp->m_features &= ~XFS_FEAT_SMALL_INUMS;
> @@ -2126,6 +2141,17 @@ xfs_fs_reconfigure(
>  		mp->m_maxagi = xfs_set_inode_alloc(mp, mp->m_sb.sb_agcount);
>  	}
> 
> +	/*
> +	 * Now that mp has been modified according to the remount options,
> +	 * we do a final option validation with xfs_finish_flags()
> +	 * just like it is done during mount. We cannot use
> +	 * xfs_finish_flags()on new_mp as it contains only the user
> +	 * given options.
> +	 */
> +	error = xfs_finish_flags(mp);
> +	if (error)
> +		return error;
> +
>  	/* ro -> rw */
>  	if (xfs_is_readonly(mp) && !(flags & SB_RDONLY)) {
>  		error = xfs_remount_rw(mp);
> --
> 2.43.5
> 
>