Re: [PATCH v2 0/6] Extend freeze support to suspend and hibernate

[James Bottomley]

On Sat, 2025-03-29 at 10:04 -0400, James Bottomley wrote:
> On Sat, 2025-03-29 at 09:42 +0100, Christian Brauner wrote:
> > Add the necessary infrastructure changes to support freezing for
> > suspend and hibernate.
> > 
> > Just got back from LSFMM. So still jetlagged and likelihood of bugs
> > increased. This should all that's needed to wire up power.
> > 
> > This will be in vfs-6.16.super shortly.
> > 
> > ---
> > Changes in v2:
> > - Don't grab reference in the iterator make that a requirement for
> > the callers that need custom behavior.
> > - Link to v1:
> > https://lore.kernel.org/r/20250328-work-freeze-v1-0-a2c3a6b0e7a6@xxxxxxxxxx
> 
> Given I've been a bit quiet on this, I thought I'd better explain
> what's going on: I do have these built, but I made the mistake of
> doing a dist-upgrade on my testing VM master image and it pulled in a
> version of systemd (257.4-3) that has a broken hibernate.  Since I
> upgraded in place I don't have the old image so I'm spending my time
> currently debugging systemd ... normal service will hopefully resume
> shortly.

I found the systemd bug

https://github.com/systemd/systemd/issues/36888

And hacked around it, so I can confirm a simple hibernate/resume works
provided the sd_start_write() patches are applied (and the hooks are
plumbed in to pm).

There is an oddity: the systemd-journald process that would usually
hang hibernate in D wait goes into R but seems to be hung and can't be
killed by the watchdog even with a -9.  It's stack trace says it's
still stuck in sb_start_write:

[<0>] percpu_rwsem_wait.constprop.10+0xd1/0x140
[<0>] ext4_page_mkwrite+0x3c1/0x560 [ext4]
[<0>] do_page_mkwrite+0x38/0xa0
[<0>] do_wp_page+0xd5/0xba0
[<0>] __handle_mm_fault+0xa29/0xca0
[<0>] handle_mm_fault+0x16a/0x2d0
[<0>] do_user_addr_fault+0x3ab/0x810
[<0>] exc_page_fault+0x68/0x150
[<0>] asm_exc_page_fault+0x22/0x30

So I think there's something funny going on in thaw.

Regards,

James