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

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Message-ID: <20200117085932.GK19428@dhcp22.suse.cz>
Date:   Fri, 17 Jan 2020 09:59:32 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Qian Cai <cai@....pw>, akpm@...ux-foundation.org,
        sergey.senozhatsky.work@...il.com, pmladek@...e.com,
        rostedt@...dmis.org, peterz@...radead.org, 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 09:51:05, David Hildenbrand wrote:
> On 17.01.20 03:21, Qian Cai wrote:
[...]
> > Even though has_unmovable_pages doesn't hold any reference to the
> > returned page this should be reasonably safe for the purpose of
> > reporting the page (dump_page) because it cannot be hotremoved. The
> 
> This is only true in the context of memory unplug, but not in the
> context of is_mem_section_removable()-> is_pageblock_removable_nolock().

Well, the above should hold for that path as well AFAICS. If the page is
unmovable then a racing hotplug cannot remove it, right? Or do you
consider a temporary unmovability to be a problem?
-- 
Michal Hocko
SUSE Labs