Re: [patch] detect and correct bad features2 superblock field

[Eric Sandeen <sandeen@sandeen.net>]

Eric Sandeen wrote:
> David Chinner wrote:
>> There is a bug in mkfs.xfs that can result in writing the features2
>> field in the superblock to the wrong location. This only occurs
>> on some architectures, typically those with 32 bit userspace and
>> 64 bit kernels.
>>
>> This patch detects the defect at mount time, logs a warning
>> such as:
>> ...
> 
>>  	/*
>> +	 * Check for a bad features2 field alignment. This happened on
>> +	 * some platforms due to xfs_sb_t not being 64bit size aligned
>> +	 * when sb_features was added and hence the compiler put it in
>> +	 * the wrong place.
>> +	 *
>> +	 * If we detect a bad field, we or the set bits into the existing
>> +	 * features2 field in case it has already been modified and we
>> +	 * don't want to lose any features. Zero the bad one and mark
>> +	 * the two fields as needing updates once the transaction subsystem
>> +	 * is online.
>> +	 */
>> +	if (xfs_sb_has_bad_features2(sbp)) {
>> +		cmn_err(CE_WARN,
>> +			"XFS: correcting sb_features alignment problem");
>> +		sbp->sb_features2 |= sbp->sb_bad_features2;
>> +		sbp->sb_bad_features2 = 0;
>> +		update_flags |= XFS_SB_FEATURES2 | XFS_SB_BAD_FEATURES2;
>> +	}
>>   
> I think there's a minor problem here that while this will update the
> superblock with the proper features2 values, features2 has already been
> checked, so mp->m_flags won't have, for example, the attr2 flags...
> 
> So attr2 will show up next time, but not on this mount.

How's this look for a fixup:

========================

[XFS]: set ATTR2 in m_flags if flag found in bad_features2

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
---


Index: linux-2.6.24.x86_64/fs/xfs/xfs_mount.c
===================================================================
--- linux-2.6.24.x86_64.orig/fs/xfs/xfs_mount.c
+++ linux-2.6.24.x86_64/fs/xfs/xfs_mount.c
@@ -1925,6 +1925,12 @@ xfs_mount_log_sb(
 	}
 	xfs_mod_sb(tp, fields);
 	xfs_trans_commit(tp, 0);
+
+	/* if we updated features2, recheck attr2 & set flag */
+	if ((fields & (XFS_SB_FEATURES2 | XFS_SB_BAD_FEATURES2)) &&
+				XFS_SB_VERSION_HASATTR2(&mp->m_sb)) {
+		mp->m_flags |= XFS_MOUNT_ATTR2;
+	}
 }