Re: [PATCH RFC] btrfs: exit scrub and balance early if the fs is being frozen

[Askar Safin <safinaskar@gmail.com>]

I just noticed that suspend behavior depends on whether "btrfs scrub" is
started in terminal window or as a systemd service. I think this is because
systemd tries to freeze user session when suspending, but doesn't freeze
services.

So I retested everything.

All tests were done with my distro's version of btrfs-progs (6.14-1).
My distro is Debian Trixie.
I have btrfs raid-1, which spans two actual partitions, 3.5 TiB each.

Let's start with unpatched v6.18-rc1.

- scrub in win, freeze_filesystems=0 - suspend doesn't work

- scrub as a service, freeze_filesystems=0 - suspend doesn't work

- scrub in win, freeze_filesystems=1
suspend takes 6-10 mins. I. e. the system hangs for 6-10 mins and then
suspends. I suspect this is time needed to complete scrub

- scrub as a service, freeze_filesystems=1 - the same

Also: on unpatched kernel "btrfs scrub" terminates instantly if it receives
INT, but doesn't terminate if it receives KILL, TERM or HUP.

Now v6.18-rc1 with your old 7 Jul 2025 patch
( https://lore.kernel.org/linux-btrfs/9606fae20bff6c1fbe14dc7b067f3b333c2a955b.1751847905.git.wqu@suse.com/ ).

- scrub in win, freeze_filesystems=0 - suspend doesn't work

- scrub as a service, freeze_filesystems=0 - suspend doesn't work

- scrub in win, freeze_filesystems=1
suspend takes 1 min. I. e. the system hangs for 1 min, then suspends

- scrub as a service, freeze_filesystems=1
suspend works perfectly. I. e. the system instantly suspends. I don't even
notice 19s delay you are talking about

Now v6.18-rc1 with your new 15 Oct 2025 patch
( https://lore.kernel.org/linux-btrfs/8c3628d5-8fce-45a1-b29c-65c2c52f1c06@gmx.com/ ).

- scrub in win, freeze_filesystems=0 - hangs for 60s, then suspends

- scrub as a service, freeze_filesystems=0 - works perfectly, i. e. suspends instantly

- scrub in win, freeze_filesystems=1 - hangs for 60s, then suspends
here is journalctl: https://zerobin.net/?7b394069a9050b8d#7PrnCDJV2t9inNFS3/EhxHJUS24iSGX7FAmjUstKKr4=

- scrub as a service, freeze_filesystems=1 - works perfectly, i. e. suspends instantly

-- 
Askar Safin