Re: [PATCH v2 1/1] xfs: Fail remount with noattr2 on a v5 with v4 enabled

["Nirjhar Roy (IBM)" <nirjhar.roy.lists@gmail.com>]

On 4/29/25 17:48, Christoph Hellwig wrote:
> On Tue, Apr 29, 2025 at 02:32:08PM +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 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@gmail.com>
>> ---
>>   fs/xfs/xfs_super.c | 25 +++++++++++++++++++++++++
>>   1 file changed, 25 insertions(+)
>>
>> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
>> index b2dd0c0bf509..1fd45567ae00 100644
>> --- a/fs/xfs/xfs_super.c
>> +++ b/fs/xfs/xfs_super.c
>> @@ -2114,6 +2114,22 @@ xfs_fs_reconfigure(
>>   	if (error)
>>   		return error;
>>   
>> +	/* attr2 -> noattr2 */
>> +	if (xfs_has_noattr2(new_mp)) {
>> +		if (xfs_has_crc(mp)) {
>> +			xfs_warn(mp, "attr2 and noattr2 cannot both be specified.");
> Nit: normal xfs style is to move the message to a new line when іt
> overflows 80 characters:
>
> 		if (xfs_has_crc(mp)) {
> 			xfs_warn(mp,
> 	"attr2 and noattr2 cannot both be specified.");
>
>> +			return -EINVAL;
>> +		}
>> +		else {
> No need for an else after a return.  And for cases where there is an
> else the kernel coding style keeps it on the same line as the closing
> brace.
>
>> +	/* 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.
>> +	 */
> Please keep comments to 80 characters.  Also the kernel coding style
> keeps the
>
> 	/*
>
> at the beginning of a comment on a separate line.

Sure, I will address the above coding style related issues. Thank you.

--NR

>
-- 
Nirjhar Roy
Linux Kernel Developer
IBM, Bangalore