Re: [PATCH AUTOSEL 4.4 08/65] btrfs: cleaner_kthread() doesn't need explicit freeze

[Sasha Levin]

On Fri, Oct 26, 2018 at 08:58:57AM +0200, Jiri Kosina wrote:
> On Thu, 25 Oct 2018, Sasha Levin wrote:
>
> > >> cleaner_kthread() is not marked freezable, and therefore calling
> > >> try_to_freeze() in its context is a pointless no-op.
> > >>
> > >> In addition to that, as has been clearly demonstrated by 80ad623edd2d
> > >> ("Revert "btrfs: clear PF_NOFREEZE in cleaner_kthread()"), it's perfectly
> > >> valid / legal for cleaner_kthread() to stay scheduled out in an arbitrary
> > >> place during suspend (in that particular example that was waiting for
> > >> reading of extent pages), so there is no need to leave any traces of
> > >> freezer in this kthread.
> > >>
> > >> Fixes: 80ad623edd2d ("Revert "btrfs: clear PF_NOFREEZE in
> > >> Fixes: cleaner_kthread()")
> > >> Fixes: 696249132158 ("btrfs: clear PF_NOFREEZE in cleaner_kthread()")
> > >> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
> > >> Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> > >> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > >
> > >IIRC it was some preparatory work for livepatching.  I did a quick check
> > >if this is safe for 4.4 and would say yes, but the patch does not fix
> > >anything so IMO this does not need to go to stable.
> >
> > Doesn't that also affect hibernation and such?
>
> This patch just removes pointless try_to_freeze(), that's guaranteed not
> to do anything and return immediately, as the btrfs kthread is not
> freezable.
> So I don't think it's needed in stable; the semantics is equivalent before
> and after.

Gotcha. I'll drop it. Thank you!

--
Thanks,
Sasha