[Bug 1901755] Re: "btrfs subvolume list" sporadically segfaults with linux-image-5.4.0-52-generic

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.

** Changed in: linux (Ubuntu)
Status: Incomplete => Confirmed

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https://bugs.launchpad.net/bugs/1901755

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

Status in linux package in Ubuntu:
Confirmed

Bug description:
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)

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