Re: Simple quota unsafe? RIP: 0010:__btrfs_free_extent.isra.0+0xc41/0x1020 [btrfs] / do_free_extent_accounting:2999: errno=-2 No such entry

[Boris Burkov <boris@bur.io>]

On Tue, Apr 14, 2026 at 10:21:55PM -0700, Marc MERLIN wrote:
> If you don't mind my asking, and even if it's just a guess:
> 
> 1) do you feel squotas are likely safe and I hit another bug?

I actually think it is a squota bug and am trying to reproduce it. I
think there may be a gap if we are deleting the qgroup in the same
transaction as the last delayed ref in the qgroup.

In meta production I have a carryover patch ignoring such enoents, which
makes me super suspicious.

I have not reproduced it yet, though.

The fact that the two stacks are in balance and qgroup deletion make me
suspicious. On the other hand, the fact that the second stack is in the
commit *before* the majority of the cleanup makes me less
suspicious.

> 2) any chance it can be block-group-tree instead? Are those 
>    considered reasonably safe? (I enabled due to the number of
>    snapshots, 100+, and being told it's bad for perf to have that
>    many, which block-group-tree is supposed to fix)

I think that is relatively unlikely.

> 3) anyone still taking bugs for btrfs check --repair since it
>    fixed nothing on an unmountable filesystem

If my suspicion is correct and this does end up being a missing qgroup I
think that I could likely have a useful fix for check --repair too.

> 4) anything useful to anyone in my broken filesystem which might
>    be easy to fix but not by me before I give up, delete it all
>    and do the multi week restore?

I think trying to dump the state of the tree on your laptop could be
quite useful.

1258303029248 is the logical address we were freeing so its backrefs in
the extent tree will be interesting. As will whatever subvol tree it is
in, as will the qgroup tree entry for that subvolid. If you can share a
full dump then I can find all that myself.

ditto for the logical address that broke on the rpi, but if that is a
gigantic fs, maybe doing the dump will be pretty unwieldy..

Thanks for your help with this,
Boris

> 
> Thanks,
> Marc
> -- 
> "A mouse is a device used to point at the xterm you want to type in" - A.S.R.
>  
> Home page: http://marc.merlins.org/                       | PGP 7F55D5F27AAF9D08