Re: qgroup rescan worker makes suspend fail

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2026/9/19 23:10, Richard Weinberger 写道:
> Once in a while, suspending my laptop just causes the screen to freeze.
> Initially, I thought Linux had crashed, but it usually recovers after 2 minutes,
> though the suspend doesn't actually happen. You can imagine this can be very
> unfortunate when you just close the laptop lid and pack the laptop into your
> bag...
> 
> After the problem started occurring more frequently, I investigated and found
> that the qgroup rescan worker is the problem. In dmesg, logs like these can
> usually be found:
> 
> [246013.777637] [ T278489] Freezing remaining freezable tasks
> [246033.780538] [ T278489] Freezing remaining freezable tasks failed after 20.003 seconds (0 tasks refusing to freeze, wq_busy=1):
> [246033.780576] [ T278489] Showing freezable workqueues that are still busy:
> [246033.780582] [ T278489] workqueue events_freezable: flags=0x104
> [246033.780590] [ T278489]   pwq 10: cpus=2 node=0 flags=0x0 nice=0 active=0 refcnt=2
> [246033.780609] [ T278489]     inactive: pci_pme_list_scan
> [246033.780642] [ T278489] workqueue btrfs-endio-meta: flags=0xe
> [246033.780649] [ T278489]   pwq 57: cpus=0-13 node=0 flags=0x4 nice=0 active=0 refcnt=2
> [246033.780660] [ T278489]     inactive: simple_end_io_work [btrfs]
> [246033.781183] [ T278489] workqueue btrfs-qgroup-rescan: flags=0x2000e
> [246033.781189] [ T278489]   pwq 56: cpus=0-13 flags=0x4 nice=0 active=1 refcnt=16
> [246033.781199] [ T278489]     in-flight: 205929:btrfs_work_helper [btrfs] for 111s
> [246033.781721] [ T278489] workqueue wg-kex-wginterproc: flags=0x6
> [246033.781726] [ T278489]   pwq 57: cpus=0-13 node=0 flags=0x4 nice=0 active=0 refcnt=2
> [246033.781736] [ T278489]     inactive: wg_packet_handshake_send_worker [wireguard]
> 
> My first thought was that the worker is likely not freezable, but it is.
> The problem is that the whole qgroup rescan is a single work item.
> In my case, such a scan can take up to 10 minutes, even though I have a
> fast NVMe SSD installed...
> 
> Wouldn't it make sense to have rescan_should_stop() return true when
> suspend starts? I think using a pm notifier could help here.
> What do you think?

Mind to try this diff? Although it requires certain pm freezing 
sequence, for now the kernel freezes the fs before processes, thus it 
should work:

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 05e35eb126dc..9ca81dfb9ee8 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3872,6 +3872,8 @@ static bool rescan_should_stop(struct 
btrfs_fs_info *fs_info)
                 return true;
         if (test_bit(BTRFS_QGROUP_RUNTIME_BIT_CANCEL_RESCAN, 
&fs_info->qgroup_flags))
                 return true;
+       if (fs_info->sb->s_writers.frozen > SB_UNFROZEN)
+               return true;
         return false;
  }

> 
> Thanks,
> //richard