services.btrfs.autoScrub: running scrub prevents system suspend

[schmittlauch]

Describe the bug

When the filesystem scrubbing service configured via services.btrfs.autoScrub is running, the system cannot suspend until the scrubbing is completed.

To Reproduce
Steps to reproduce the behavior:

1. enable the autoscrub service on some Btrfs file system, e.g. by

services.btrfs.autoScrub = {enable = true; fileSystems = [ "/" ];};

2. start the resulting service, e.g. systemctl start btrfs-scrub-.service
3. suspend-to-ram the system: systemctl suspend
4. the system fails to suspend and a trace appropriating this failure tu btrfs can be found in the system journal

Expected behavior

The scrub should be paused properly when the system suspends.

More context

It's likely that this is an upstream bug. I'll ask around on the btrfs mailing list and will update this issue accordingly.

Metadata

• system: "x86_64-linux"
• host os: Linux 4.19.98, NixOS, 19.09.1970.6d9a4a615ee (Loris)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.3.2
• channels(root): "home-manager-19.09, nixos-19.09.1970.6d9a4a615ee, nixos-unstable-20.03pre210639.e59dcf8ccec"
• channels(user): "home-manager-19.09"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module:
- tasks/filesystems/btrfs.nix

[symphorien]

The service probably needs Conflicts=suspend.target sleep.target and the other suspend related targets.

[schmittlauch]

The issue still appears with a 5.4 kernel.

system journal