Can’t mount XFS filesystem from a partition after upgrade to 4.2

[duncancmt]

Qubes OS release

4.2.1

Brief summary

Prior to upgrading to 4.2, I was able to mount a partition inside a VM. Now I am not. This is a separate partition on the same NVMe drive as my Qubes BTRFS root. Surprisingly, the partition mounts just fine in dom0.

https://forum.qubes-os.org/t/cant-mount-xfs-filesystem-from-a-partition-after-upgrade-to-4-2/26809

Steps to reproduce

Create partition. Format as XFS. Attempt to mount in a VM

Expected behavior

It should mount

Actual behavior

Error thrown

$ sudo mount -t xfs /dev/xvdi /mnt/mountpoint
mount: /mnt/mountpoint: can't read superblock on /dev/xvdi.
       dmesg(1) may have more information after failed mount system call.
$ sudo dmesg
<snip>
[ 1825.885414] blkfront: xvdi: flush diskcache: enabled; persistent grants: enabled; indirect descriptors: enabled; bounce buffer: enabled
[ 1837.175245] SGI XFS with ACLs, security attributes, realtime, scrub, quota, no debug enabled
[ 1837.176949] I/O error, dev xvdi, sector 0 op 0x0:(READ) flags 0x1000 phys_seg 1 prio class 0
[ 1837.176996] XFS (xvdi): SB validate failed with error -5.

[rustybird]

This is a separate partition on the same NVMe drive as my Qubes BTRFS root.

Using the same setup, I haven't been able to reproduce this problem.

Steps to reproduce

Create partition. Format as XFS.

Can you post the exact dom0 commands? The qvm-block attach command too.

[ 1837.176949] I/O error, dev xvdi, sector 0 op 0x0:(READ) flags 0x1000 phys_seg 1 prio class 0

Odd. Are you by any chance involving dm-integrity somehow, especially cryptsetup luksFormat --integrity-no-wipe?

[duncancmt]

I apologize for the glibness of the steps to reproduce. I partitioned this drive quite a while ago, so I don't have the exact commands I ran. It was something along the lines of using gdisk to partition in dom0 and:

$ sudo mkfs.xfs -f -m bigtime=1 -m rmapbt=1 -m reflink=1 /dev/xvdi

to format the drive inside the VM. This is the same SSD that holds dom0's root and boot (root is btrfs, encrypted of course; in this case LUKS2 xchacha12,aes-adiantum-plain64, no integrity), but the badly-behaved partition is just that: a partition. It's not a btrfs subvolume.

---

As far as commands I use to attempt to mount the drive:

dom0

$ qvm-block attach ethereum dom0:nvme0n1p4
$ echo $?
0

ethereum

$ sudo mount -m /dev/xvdi /mnt/ethereum
mount: /mnt/ethereum: can't read superblock on /dev/xvdi.
       dmesg(1) may have more information after failed mount system call.
$ sudo dmesg
<snip>
[   44.598154] SGI XFS with ACLs, security attributes, realtime, scrub, quota, no debug enabled
[   44.602523] I/O error, dev xvdi, sector 0 op 0x0:(READ) flags 0x1000 phys_seg 1 prio class 0
[   44.602582] XFS (xvdi): SB validate failed with error -5.

---

Then I can detach the volume from the ethereum VM, shut it down, and back in dom0 run:

$ sudo mount -m /dev/nvme0n1p4 /mnt/ethereum
$ echo $?
0
$ ls /mnt/ethereum
<some files>

---

Odd. Are you by any chance involving dm-integrity somehow, especially cryptsetup luksFormat --integrity-no-wipe?

As implied by the commands above, this is just a bare partition that has been formatted XFS. No RAID. No LUKS. No integrity.

And for the record, I get the same behavior on Fedora 38, Fedora 39, and Debian 12.

[rustybird]

Are there any dom0 kernel messages during the period where you are attaching the partition and attempting to mount it inside the VM?

I also wonder if it's possible to take XFS out of the equation: If you attach the partition and run something like sudo head -c 100M /dev/xvdi | sha256sum does it result in the same read error?

[duncancmt]

$ sudo dd if=/dev/xvdi of=/dev/null bs=1 count=1M status=progress
1048576+0 records in
1048576+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.440201 s, 2.4 MB/s
$ echo $?
0

dmesg shows nothing of note

$ sudo mount -m /dev/xvdi /mnt/ethereum
mount: /mnt/ethereum: can't read superblock on /dev/xvdi.
       dmesg(1) may have more information after failed mount system call.
$ sudo dmesg
<snip>
[   68.055045] SGI XFS with ACLs, security attributes, realtime, scrub, quota, no debug enabled
[   68.057308] I/O error, dev xvdi, sector 0 op 0x0:(READ) flags 0x1000 phys_seg 1 prio class 0
[   68.057333] XFS (xvdi): SB validate failed with error -5.
$ sudo head -c 100M /dev/xvdi | sha256sum
REDACTED  -
$ echo $?
0

so it appears to be XFS-specific

and for what it's worth, shasum-ing the first 100M of the partition in dom0 returns the same hash

[duncancmt]

The only logline in dom0 dmesg that appears during the process is (sorry hand copied):

[206838.262156] xen-blkback: backend/vbd/15/51840: using 4 queues, protocol 1 (x86_64-abi) persistent grants

which seems uninteresting

[rustybird]

This is so intriguing! I'm out of ideas though :(

Maybe try the linux-xfs mailing list?

[rustybird]

Apparently I'm now experiencing the issue myself: A read error at sector 0 happening only when I attempt to mount the attached block device, but not otherwise. However my block device contains an ext4 filesystem instead of XFS.

This has occurred almost all the time with kernel-latest-qubes-vm (6.9.4 and 6.9.2). I haven't been able to reproduce it with kernel-qubes-vm (6.6.33) so far.

[rustybird]

My source device in dom0 is a loop device with 4096 byte logical+physical block size, which in the failing case is attached to the VM with 512 byte logical+physical blocks. Can you try this in your setup (substituting your NVMe device for my loop12 device) @duncancmt?

[user@dom0 ~]$ head /sys/block/loop12/queue/*_block_size
==> /sys/block/loop12/queue/logical_block_size <==
4096

==> /sys/block/loop12/queue/physical_block_size <==
4096

[user@dom0 bin]$ qvm-run -p the-vm 'head /sys/block/xvdi/queue/*_block_size'
==> /sys/block/xvdi/queue/logical_block_size <==
512

==> /sys/block/xvdi/queue/physical_block_size <==
512

[rustybird]

read error at sector 0 happening only when I attempt to mount the attached block device, but not otherwise

The discrepancy is due to the read during the mount attempt happening with direct I/O turned on. I also get it for dd if=/dev/xvdi of=/dev/null count=1 with vs. without iflag=direct

[marmarek]

Kernel regression then?

[rustybird]

Yeah, last good one appears to be 6.8.8-1. Unfortunately kernel-latest 6.9.2-1 is already in stable :(

[duncancmt]

Can you try this in your setup?

[user@dom0 ~]$ head /sys/block/nvme0n1/queue/*_block_size
==> /sys/block/nvme0n1/queue/logical_block_size <==
4096

==> /sys/block/nvme0n1/queue/physical_block_size <==
4096

[user@dom0 ~]$ qvm-run -p ethereum 'head /sys/block/xvdi/queue/*_block_size'
==> /sys/block/xvdi/queue/logical_block_size <==
4096

==> /sys/block/xvdi/queue/physical_block_size <==
4096

so that's different :thinking:

I also get it for dd if=/dev/xvdi of=/dev/null count=1 with vs. without iflag=direct

[user@ethereum ~]$ sudo dd if=/dev/xvdi of=/dev/null bs=1 count=1 status=progress
1+0 records in
1+0 records out
1 byte copied, 0.0119412 s, 0.1 kB/s
[user@ethereum ~]$ sudo dd if=/dev/xvdi of=/dev/null bs=1 count=1 status=progress iflag=direct
/usr/bin/dd: error reading '/dev/xvdi': Invalid argument
0+0 records in
0+0 records out
0 bytes copied, 2.7803e-05 s, 0.0 kB/s

so that's different as well

EDIT: I get the same error in dom0 with iflag=direct; setting bs=4096 makes dd happy, but bs=512 does not

[duncancmt]

Oh wait. I got ahead of myself and downgraded the troublesome VM to 6.8.8-1. With the vm on 6.9.2-1, I get:

[user@dom0 ~]$ qvm-run -p ethereum 'head /sys/block/xvdi/queue/*_block_size'
==> /sys/block/xvdi/queue/logical_block_size <==
512

==> /sys/block/xvdi/queue/physical_block_size <==
512

[user@ethereum ~]$ sudo dd if=/dev/xvdi of=/dev/null count=1 status=progress
1+0 records in
1+0 records out
512 bytes copied, 0.00148875 s, 344 kB/s
[user@ethereum ~]$ sudo dd if=/dev/xvdi of=/dev/null count=1 status=progress iflag=direct
/usr/bin/dd: error reading '/dev/xvdi': Input/output error
0+0 records in
0+0 records out
0 bytes copied, 0.000170858 s, 0.0 kB/s
[user@ethereum ~]$ sudo dd if=/dev/xvdi of=/dev/null bs=4096 count=1 status=progress iflag=direct
1+0 records in
1+0 records out
4096 bytes (4.1 kB, 4.0 KiB) copied, 0.011916 s, 344 kB/s

[marmarek]

What about adding bs=4096 ? Does it change anything?

-- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab

[rustybird]

Oh wait. I got ahead of myself and downgraded the troublesome VM to 6.8.8-1. With the vm on 6.9.2-1, I get:

Thank God :laughing:

There were 5 commits to xen-blkfront.c in February that all landed in kernel 6.9. The last one has logical/physical block size stuff in the diff, although the first one is already related to queue limits.

[marmarek]

Thanks @rustybird ! I've forwarded the info to relevant maintainers: https://lore.kernel.org/xen-devel/Znl5FYI9CC37jJLX@mail-itl/T/#u

[marmarek]

@rustybird @duncancmt the above linked thread has a proposed fix from Christoph Hellwig already, care to try (and preferably report back in the email thread)?

[rustybird]

Welp, I can't even get builderv2 to download the repo (there's a different number of missing bytes every time):

15:35:15,176 [executor:local:/home/user/tmp/138233767774496c9ed3ed0/builder] output: args: (128, ['git', 'clone', '-n', '-q', '-b', 'main', 'https://github.com/QubesOS/qubes-linux-kernel', '/home/user/tmp/138233767774496c9ed3ed0/builder/linux-kernel-latest'])
15:35:15,177 [executor:local:/home/user/tmp/138233767774496c9ed3ed0/builder] output: stdout: b''
15:35:15,177 [executor:local:/home/user/tmp/138233767774496c9ed3ed0/builder] output: stderr: b'error: 3213 bytes of body are still expected\nfetch-pack: unexpected disconnect while reading sideband packet\nfatal: early EOF\nfatal: fetch-pack: invalid index-pack output\n'

Maybe I can just build the xen_blkfront module manually somehow.

Edit: Managed to download the repo and everything, it's building

Edit 2: The patch works: https://lore.kernel.org/xen-devel/Znndj9W_bCsFTxkz@mutt/

[qubesos-bot]

Automated announcement from builder-github

The component linux-kernel-latest (including package kernel-latest-6.9.7-1.qubes.fc32) has been pushed to the r4.1 testing repository for dom0. To test this update, please install it with the following command:

sudo qubes-dom0-update --enablerepo=qubes-dom0-current-testing

Changes included in this update

[qubesos-bot]

Automated announcement from builder-github

The component linux-kernel-latest (including package kernel-latest-6.9.7-1.qubes.fc32) has been pushed to the r4.1 stable repository for dom0. To install this update, please use the standard update command:

sudo qubes-dom0-update

Or update dom0 via Qubes Manager.

Changes included in this update