On Mon, Mar 29, 2021 at 1:34 AM B A [off-list ref] wrote:

This is a very old BTRFS filesystem created with Fedora *23* i.e. a linux kernel and btrfs-progs around version 4.2. It was probably created 2015-10-31 with Fedora 23 beta and kernel 4.2.4 or 4.2.5.

I ran `btrfs scrub` about a month ago without issues. I ran `btrfs check` maybe a year ago without issues. I also run `btrfs filesystem balance` from time to time (~once a year). None of these have shown the issue before. Does that mean that the issue has not been present for a long time (>1 year)?

Maybe. The generation on these two leaves look recent. But kernels
since ~5.3 have a write time tree checker designed to catch metadata
errors before they are written.

What do you get for:

btrfs insp dump-s -f /dev/dm-0

Hopefully Qu or Josef will have an idea.

--
Chris Murphy