Re: [btrfs] commit bc27d6f0aa0e4de184b617aceeaf25818cc646de breaks update-grub

[Anand Jain]

On 11/01/2024 22:36, David Sterba wrote:
> On Thu, Jan 11, 2024 at 04:50:56PM +0100, David Sterba wrote:
> > On Thu, Jan 11, 2024 at 12:45:50PM +0100, Thorsten Leemhuis wrote:
> > > [Adding Anand Jain, the author of the culprit to the list of recipients;
> > > furthermore CCing the the Btrfs maintainers and the btrfs list; also
> > > CCing regression list, as it should be in the loop for regressions:
> > > https://docs.kernel.org/admin-guide/reporting-regressions.html]
> > >
> > > On 08.01.24 15:11, Alex Romosan wrote:
> > > > Please Cc me as I am not subscribed to the list.
> > > >
> > > > Running my own compiled kernel without initramfs on a lenovo thinkpad
> > > > x1 carbon gen 7.
> > > >
> > > > Since version 6.7-rc1 i haven't been able to to a grub-update,
> > > >
> > > > instead i get this error:
> > > >
> > > > grub-probe: error: cannot find a device for / (is /dev mounted?) solid
> > > > state drive
> > > >
> > > > 6.6 was the last version that worked.
> > > >
> > > > Today I did a git-bisect between these two versions which identified
> > > > commit bc27d6f0aa0e4de184b617aceeaf25818cc646de btrfs: scan but don't
> > > > register device on single device filesystem as the culprit. reverting
> > > > this commit from 6.7 final allowed me to run update-grub again.
> > > >
> > > > not sure if this is the intended behavior or if i'm missing some other
> > > > kernel options. any help/fixes would be appreciated.
> > > >
> > > > thank you.
> > >
> > > Thanks for the report. To be sure the issue doesn't fall through the
> > > cracks unnoticed, I'm adding it to regzbot, the Linux kernel regression
> > > tracking bot:
> > >
> > > #regzbot ^introduced bc27d6f0aa0e4de184b617aceeaf25818cc646de
> > > #regzbot title btrfs: update-grub broken (cannot find a device for / (is
> > > /dev mounted?))
> > > #regzbot ignore-activity
> >
> > The bug is also tracked at https://bugzilla.kernel.org/show_bug.cgi?id=218353 .
>
> About the fix: we can't simply revert the patch because the temp_fsid
> depends on that. A workaround could be to check if the device path is
> "/dev/root" and still register the device. But I'm not sure if this does
> not break the use case that Steamdeck needs, as it's for the root
> partition.


Thank you for the report.

The issue seems more complex than a simple scenario, as the following
test-case works well:

  $ mount /dev/sdb1 /btrfs
  $ cat /proc/self/mountinfo | grep btrfs
345 63 0:34 / /btrfs rw,relatime shared:179 - btrfs /dev/sdb1 
rw,space_cache=v2,subvolid=5,subvol=/

However, the relevant part of the commit
bc27d6f0aa0e4de184b617aceeaf25818cc646de that may be failing could
be in identifying a device, whether it is the same or different
For this, we use:

     lookup_bdev(path, &path_devt);

and match with the devt(MAJ:MIN) saved in the btrfs_device;
would this work during initrd? I need to dig more. Trying
to figure out how can I reproduce this.

Thanks, Anand