linux-kernel - Re: [PATCH -next v4] mm/hotplug: silence a lockdep splat with printk()

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Message-ID: <20200117154657.GL19428@dhcp22.suse.cz>
Date:   Fri, 17 Jan 2020 16:46:57 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Qian Cai <cai@....pw>
Cc:     akpm@...ux-foundation.org, sergey.senozhatsky.work@...il.com,
        pmladek@...e.com, rostedt@...dmis.org, peterz@...radead.org,
        david@...hat.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v4] mm/hotplug: silence a lockdep splat with
 printk()

On Fri 17-01-20 10:05:12, Qian Cai wrote:
> 
> 
> > On Jan 17, 2020, at 9:39 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > 
> > Thanks a lot. Having it in a separate patch would be great.
> 
> I was thinking about removing that WARN together in this v5 patch,
> so there is less churn to touch the same function again. However, I
> am fine either way, so just shout out if you feel strongly towards a
> separate patch.

I hope you meant moving rather than removing ;). The warning is useful
because we shouldn't see unmovable pages in the movable zone. And a
separate patch makes more sense because the justification is slightly
different. We do not want to have a way for userspace to trigger the
warning from userspace - even though it shouldn't be possible, but
still. Only the offlining path should complain.

-- 
Michal Hocko
SUSE Labs