linux-kernel - Re: [PATCH AUTOSEL 4.4 08/65] btrfs: cleaner

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Date:   Thu, 25 Oct 2018 17:07:29 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH AUTOSEL 4.4 08/65] btrfs: cleaner_kthread() doesn't need
 explicit freeze

On Thu, Oct 25, 2018 at 10:16:08AM -0400, Sasha Levin wrote:
> From: Jiri Kosina <jkosina@...e.cz>
> 
> [ Upstream commit 838fe1887765f4cc679febea60d87d2a06bd300e ]
> 
> 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 cleaner_kthread()")
> Fixes: 696249132158 ("btrfs: clear PF_NOFREEZE in cleaner_kthread()")
> Signed-off-by: Jiri Kosina <jkosina@...e.cz>
> Signed-off-by: David Sterba <dsterba@...e.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

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.