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

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Message-ID: <06e740ad-8990-45ca-bdd8-fa5d446e4bd4@gmail.com>
Date: Mon, 12 May 2025 17:32:10 +0530
From: "Nirjhar Roy (IBM)" <nirjhar.roy.lists@...il.com>
To: Carlos Maiolino <cem@...nel.org>
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 5/12/25 16:40, Carlos Maiolino wrote:
> 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.
Sure.
>
>
> 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.

Okay. I will keep this in mind.

--NR

>
>
>> +		}
>> +		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
>>
>>
-- 
Nirjhar Roy
Linux Kernel Developer
IBM, Bangalore