"btrfs subvolume list" sporadically segfaults with linux-image-5.4.0-52-generic

[Martin Carpella]

On a BTRFS volume with a lot of subvolumes, I get sporadic segfaults on "btrfs subvolume list", about 1/3 of the time. This is on Ubuntu 20.04.

linux-image-5.4.0-48-generic does not experience those segfaults.

On #btrfs on freenode, it was pointed out that 5.4.0-52.57 seems to have a regression but not the fix for it committed. To quote from the IRC message:

> 5.4.0-52.57 has a regression (a48b73eca4ce btrfs: fix potential deadlock in the search ioctl) and not the fix (1c78544eaa46 btrfs: fix wrong address when faulting in pages in the search ioctl)

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1901755

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Martin Carpella (martinc)]

I'm currently not running the affected kernel version, since the system is being used as a backup-target (hence the high subvolume count), therefore I cannot provide the requested log.

My initial bug report contains the information that should help determining which commit is missing from the kernel.

[Po-Hsu Lin (cypressyew)]

Hello Martin,

thanks for your bug report, the fix mentioned in the quote (1c78544eaa46 btrfs: fix wrong address when faulting in pages in the search ioctl) has already been applied to the Focal master-next branch via stable update process in bug 1896824.

It's expected to have this fix available in -updates after the upcoming SRU cycle.

I will keep this report open to make it easier for others to find it.

[David A. Sjøen (dabide)]

Hello Po-Hsu Lin,

Will this also be fixed in the current 18.04 kernel, or has it already been? We have the same issue there.

David

[Bastian Baum (protree)]

I'm still getting this error on Ubuntu 18.04 with kernel 5.4.0-54.60. Installed Mainline Kernel 5.9.10 as a workaround...

[Po-Hsu Lin (cypressyew)]

Hi all,
with commit 1c78544eaa46 in Focal[1] tree released, this fix should be available since Ubuntu-5.4.0-55.61

~/ubuntu-focal [master-next]$ git tag --contains 0d3fe387a7a4da52e94d960eb0987b991b29dbdf
Ubuntu-5.4.0-55.61
Ubuntu-5.4.0-56.62
Ubuntu-5.4.0-57.63
Ubuntu-5.4.0-58.64
Ubuntu-5.4.0-59.65
Ubuntu-5.4.0-60.67
Ubuntu-5.4.0-61.69
Ubuntu-5.4.0-62.70
Ubuntu-5.4.0-64.72
Ubuntu-5.4.0-65.73
Ubuntu-5.4.0-66.74
Ubuntu-5.4.0-67.75
Ubuntu-5.4.0-68.76

For Bionic, you can get this fix with the 5.4 HWE kernel on bionic.

Therefore I am closing this bug here, please feel free to open a new issue with command "ubuntu-bug linux".
Thanks

[1] https://kernel.ubuntu.com/git/ubuntu/ubuntu-focal.git/commit/?id=0d3fe387a7a4da52e94d960eb0987b991b29dbdf