Comment 5 for bug 1906476

This issue seems to have appeared somewhere between zfs-linux 0.8.4-1ubuntu11 (last known working version) and 0.8.4-1ubuntu16.

When the issue first hit, I had zfs-dkms installed, which was on 0.8.4-1ubuntu16 where as the kernel build had 0.8.4-1ubuntu11. I removed zfs-dkms to go back to the kernel built version and it was working OK. linux-image-5.8.0-36-generic is now released on Hirsute with 0.8.4-1ubuntu16 and so now the out of the box kernel is also broken and I am regularly having problems with this.

linux-image-5.8.0-29-generic: working
linux-image-5.8.0-36-generic: broken

`
lathiat@optane ~/src/zfs[zfs-2.0-release]$ sudo modinfo /lib/modules/5.8.0-29-generic/kernel/zfs/zfs.ko|grep version
version: 0.8.4-1ubuntu11

lathiat@optane ~/src/zfs[zfs-2.0-release]$ sudo modinfo /lib/modules/5.8.0-36-generic/kernel/zfs/zfs.ko|grep version
version: 0.8.4-1ubuntu16
`

I don't have a good quick/easy reproducer but just using my desktop for a day or two seems I am likely to hit the issue after a while.

I tried to install the upstream zfs-dkms package for 2.0 to see if I can bisect the issue on upstream versions but it breaks my boot for some weird systemd reason I cannot quite figure out as yet.

Looking at the Ubuntu changelog I'd say the fix for https://bugs.launchpad.net/bugs/1899826 that landed in 0.8.4-1ubuntu13 to backport the 5.9 and 5.10 compataibility patches is a prime suspect but could also be any other version. I'm going to try and 'bisect' 0.8.4-1ubuntu11 through 0.8.4-1ubuntu16 to figure out which version actually hit it.

Since the default kernel is now hitting this, there have been 2 more user reports of the same things in the upstream bug in the past few days since that kernel landed and I am regularly getting inaccessible files not just from chrome but even a linux git tree among other things I am going to raise the priority on this bug to Critical as you lose access to files so has data loss potential. I have not yet determined if you can somehow get the data back, so far it's only affected files I can replace such as cache/git files. It seems like snapshots might be OK (which would make sense).