On Wed, Feb 14, 2024 at 7:17 AM David Sterba <dsterba@xxxxxxx> wrote:
>
> On Tue, Feb 13, 2024 at 09:13:56AM +0800, Anand Jain wrote:
> > There are reports that since version 6.7 update-grub fails to find the
> > device of the root on systems without initrd and on a single device.
> >
> > This looks like the device name changed in the output of
> > /proc/self/mountinfo:
> >
> > 6.5-rc5 working
> >
> > 18 1 0:16 / / rw,noatime - btrfs /dev/sda8 ...
> >
> > 6.7 not working:
> >
> > 17 1 0:15 / / rw,noatime - btrfs /dev/root ...
> >
> > and "update-grub" shows this error:
> >
> > /usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?)
> >
> > This looks like it's related to the device name, but grub-probe
> > recognizes the "/dev/root" path and tries to find the underlying device.
> > However there's a special case for some filesystems, for btrfs in
> > particular.
> >
> > The generic root device detection heuristic is not done and it all
> > relies on reading the device infos by a btrfs specific ioctl. This ioctl
> > returns the device name as it was saved at the time of device scan (in
> > this case it's /dev/root).
> >
> > The change in 6.7 for temp_fsid to allow several single device
> > filesystem to exist with the same fsid (and transparently generate a new
> > UUID at mount time) was to skip caching/registering such devices.
> >
> > This also skipped mounted device. One step of scanning is to check if
> > the device name hasn't changed, and if yes then update the cached value.
> >
> > This broke the grub-probe as it always read the device /dev/root and
> > couldn't find it in the system. A temporary workaround is to create a
> > symlink but this does not survive reboot.
> >
> > The right fix is to allow updating the device path of a mounted
> > filesystem even if this is a single device one.
> >
> > In the fix, check if the device's major:minor number matches with the
> > cached device. If they do, then we can allow the scan to happen so that
> > device_list_add() can take care of updating the device path. The file
> > descriptor remains unchanged.
> >
> > This does not affect the temp_fsid feature, the UUID of the mounted
> > filesystem remains the same and the matching is based on device major:minor
> > which is unique per mounted filesystem.
> >
> > This covers the path when the device (that exists for all mounted
> > devices) name changes, updating /dev/root to /dev/sdx. Any other single
> > device with filesystem and is not mounted is still skipped.
> >
> > Note that if a system is booted and initial mount is done on the
> > /dev/root device, this will be the cached name of the device. Only after
> > the command "btrfs device scan" it will change as it triggers the
> > rename.
> >
> > The fix was verified by users whose systems were affected.
> >
> > CC: stable@xxxxxxxxxxxxxxx # 6.7+
> > Fixes: bc27d6f0aa0e ("btrfs: scan but don't register device on single device filesystem")
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=218353
> > Link: https://lore.kernel.org/lkml/CAKLYgeJ1tUuqLcsquwuFqjDXPSJpEiokrWK2gisPKDZLs8Y2TQ@xxxxxxxxxxxxxx/
> > Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
> > Tested-by: Alex Romosan <aromosan@xxxxxxxxx>
> > Tested-by: CHECK_1234543212345@xxxxxxxxxxxxxx
>
> Reviewed-by: David Sterba <dsterba@xxxxxxxx>
>
> When you commit the patch, please reorder the tags according to
> https://btrfs.readthedocs.io/en/latest/dev/Developer-s-FAQ.html#ordering
So this introduces a regression.
Running fstests:
(...)
btrfs/156 11s ... 16s
btrfs/157 3s ... 0s
btrfs/158 0s ... 2s
btrfs/159 16s ... - output mismatch (see
/home/fdmanana/git/hub/xfstests/results//btrfs/159.out.bad)
--- tests/btrfs/159.out 2020-10-26 15:31:57.061207266 +0000
+++ /home/fdmanana/git/hub/xfstests/results//btrfs/159.out.bad
2024-02-20 12:54:43.386131546 +0000
@@ -1,8 +1,11 @@
QA output created by 159
+mount: /home/fdmanana/btrfs-tests/scratch_1: wrong fs type, bad
option, bad superblock on /dev/mapper/flakey-test, missing codepage or
helper program, or other error.
+ dmesg(1) may have more information after failed mount system call.
File digest before power failure:
-f049865ed45b1991dc9a299b47d51dbf SCRATCH_MNT/foobar
+b2e8facfb4795185fadd85707fe78973 SCRATCH_MNT/foobar
+umount: /home/fdmanana/btrfs-tests/scratch_1: not mounted.
...
(Run 'diff -u /home/fdmanana/git/hub/xfstests/tests/btrfs/159.out
/home/fdmanana/git/hub/xfstests/results//btrfs/159.out.bad' to see
the entire diff)
btrfs/160 4s ... 4s
(...)
The weird thing is it doesn't happen when running btrfs/159 standalone
(even if doing a rmmod btrfs before).
Instead of running all tests, I managed to reproduce it with only:
$ ./check btrfs/14[6-9] btrfs/15[8-9]
FSTYP -- btrfs
PLATFORM -- Linux/x86_64 debian0 6.8.0-rc5-btrfs-next-151+ #1 SMP
PREEMPT_DYNAMIC Mon Feb 19 13:38:37 WET 2024
MKFS_OPTIONS -- /dev/sdc
MOUNT_OPTIONS -- /dev/sdc /home/fdmanana/btrfs-tests/scratch_1
btrfs/146 1s ... 2s
btrfs/147 0s ... 1s
btrfs/148 2s ... 2s
btrfs/149 1s ... 1s
btrfs/158 1s ... 0s
btrfs/159 20s ... - output mismatch (see
/home/fdmanana/git/hub/xfstests/results//btrfs/159.out.bad)
--- tests/btrfs/159.out 2020-10-26 15:31:57.061207266 +0000
+++ /home/fdmanana/git/hub/xfstests/results//btrfs/159.out.bad
2024-02-20 13:51:25.707220763 +0000
@@ -1,8 +1,11 @@
QA output created by 159
+mount: /home/fdmanana/btrfs-tests/scratch_1: wrong fs type, bad
option, bad superblock on /dev/mapper/flakey-test, missing codepage or
helper program, or other error.
+ dmesg(1) may have more information after failed mount system call.
File digest before power failure:
-f049865ed45b1991dc9a299b47d51dbf SCRATCH_MNT/foobar
+b2e8facfb4795185fadd85707fe78973 SCRATCH_MNT/foobar
+umount: /home/fdmanana/btrfs-tests/scratch_1: not mounted.
...
(Run 'diff -u /home/fdmanana/git/hub/xfstests/tests/btrfs/159.out
/home/fdmanana/git/hub/xfstests/results//btrfs/159.out.bad' to see
the entire diff)
Ran: btrfs/146 btrfs/147 btrfs/148 btrfs/149 btrfs/158 btrfs/159
dmesg shows:
[79195.239769] run fstests btrfs/159 at 2024-02-20 14:06:02
[79195.418917] BTRFS: device fsid 45ac9151-7e2d-4dd7-bf75-99967f869f2a
devid 1 transid 3747 /dev/sdb scanned by mount (3413231)
[79195.419515] BTRFS info (device sdb): first mount of filesystem
45ac9151-7e2d-4dd7-bf75-99967f869f2a
[79195.419525] BTRFS info (device sdb): using crc32c (crc32c-intel)
checksum algorithm
[79195.419529] BTRFS info (device sdb): using free-space-tree
[79195.612719] BTRFS: device fsid 10184d7d-3ca9-43c1-a6f8-70b134cff828
devid 1 transid 6 /dev/sdc scanned by mkfs.btrfs (3413318)
[79195.666279] BTRFS: device fsid 10184d7d-3ca9-43c1-a6f8-70b134cff828
devid 1 transid 6 /dev/dm-0 scanned by systemd-udevd (3410982)
[79195.695774] BTRFS info (device dm-0): first mount of filesystem
10184d7d-3ca9-43c1-a6f8-70b134cff828
[79195.695786] BTRFS info (device dm-0): using crc32c (crc32c-intel)
checksum algorithm
[79195.695789] BTRFS error (device dm-0): superblock fsid doesn't
match fsid of fs_devices: 10184d7d-3ca9-43c1-a6f8-70b134cff828 !=
628aff33-4122-4d77-b2a9-2e9a90f27520
[79195.696098] BTRFS error (device dm-0): superblock metadata_uuid
doesn't match metadata uuid of fs_devices:
10184d7d-3ca9-43c1-a6f8-70b134cff828 !=
628aff33-4122-4d77-b2a9-2e9a90f27520
[79195.696419] BTRFS error (device dm-0): dev_item UUID does not match
metadata fsid: 628aff33-4122-4d77-b2a9-2e9a90f27520 !=
10184d7d-3ca9-43c1-a6f8-70b134cff828
[79195.696765] BTRFS error (device dm-0): superblock contains fatal errors
[79195.697447] BTRFS error (device dm-0): open_ctree failed
It always happens with this patch applied in for-next, and never
happens with it reverted.
>
