linux-kernel - XFS attr2 mount option removal may break system boot

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Message-ID: <3654080.iIbC2pHGDl@natalenko.name>
Date: Mon, 13 Oct 2025 21:08:38 +0200
From: Oleksandr Natalenko <oleksandr@...alenko.name>
To: linux-kernel@...r.kernel.org
Cc: linux-xfs@...r.kernel.org, Carlos Maiolino <cem@...nel.org>,
 "Darrick J. Wong" <djwong@...nel.org>, Pavel Reichl <preichl@...hat.com>,
 Vlastimil Babka <vbabka@...e.cz>, Thorsten Leemhuis <linux@...mhuis.info>
Subject: XFS attr2 mount option removal may break system boot

Hello.

In v6.18, the attr2 XFS mount option is removed. This may silently break system boot if the attr2 option is still present in /etc/fstab for rootfs.

Consider Arch Linux that is being set up from scratch with / being formatted as XFS. The genfstab command that is used to generate /etc/fstab produces something like this by default:

/dev/sda2 on / type xfs (rw,relatime,attr2,discard,inode64,logbufs=8,logbsize=32k,noquota)

Once the system is set up and rebooted, there's no deprecation warning seen in the kernel log:

# cat /proc/cmdline
root=UUID=77b42de2-397e-47ee-a1ef-4dfd430e47e9 rootflags=discard rd.luks.options=discard quiet

# dmesg | grep -i xfs
[    2.409818] SGI XFS with ACLs, security attributes, realtime, scrub, repair, quota, no debug enabled
[    2.415341] XFS (sda2): Mounting V5 Filesystem 77b42de2-397e-47ee-a1ef-4dfd430e47e9
[    2.442546] XFS (sda2): Ending clean mount

Although as per the deprecation intention, it should be there.

Vlastimil (in Cc) suggests this is because xfs_fs_warn_deprecated() doesn't produce any warning by design if the XFS FS is set to be rootfs and gets remounted read-write during boot. This imposes two problems:

1) a user doesn't see the deprecation warning; and
2) with v6.18 kernel, the read-write remount fails because of unknown attr2 option rendering system unusable:

systemd[1]: Switching root.
systemd-remount-fs[225]: /usr/bin/mount for / exited with exit status 32.

# mount -o rw /
mount: /: fsconfig() failed: xfs: Unknown parameter 'attr2'.

Thorsten (in Cc) suggested reporting this as a user-visible regression.

>From my PoV, although the deprecation is in place for 5 years already, it may not be visible enough as the warning is not emitted for rootfs. Considering the amount of systems set up with XFS on /, this may impose a mass problem for users.

Vlastimil suggested making attr2 option a complete noop instead of removing it.

Please check.

Thank you.

-- 
Oleksandr Natalenko, MSE
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