linux-ext4 - [PATCH v3 1/1] xfs: Fail remount with noattr2 on a v5 with v4 enabled

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Message-ID: <a56bb4685df5f8f45308f6a3195390ad73b75709.1745937794.git.nirjhar.roy.lists@gmail.com>
Date: Tue, 29 Apr 2025 20:17:59 +0530
From: "Nirjhar Roy (IBM)" <nirjhar.roy.lists@...il.com>
To: linux-xfs@...r.kernel.org
Cc: 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,
	nirjhar.roy.lists@...il.com
Subject: [PATCH v3 1/1] xfs: Fail remount with noattr2 on a v5 with v4 enabled

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>
---
 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..58a0431ab52d 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 and noattr2 cannot both be specified.");
+			return -EINVAL;
+		}
+		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