linux-kernel - Re: uninitialized pmem struct pages

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Message-ID: <20210105075028.GS13207@dhcp22.suse.cz>
Date:   Tue, 5 Jan 2021 08:50:28 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: uninitialized pmem struct pages

On Mon 04-01-21 21:17:43, Dan Williams wrote:
> On Mon, Jan 4, 2021 at 2:45 AM David Hildenbrand <david@...hat.com> wrote:
[...]
> > I believe Dan mentioned somewhere that he wants to see a real instance
> > of this producing a BUG before actually moving forward with a fix. I
> > might be wrong.
> 
> I think I'm missing an argument for the user-visible effects of the
> "Bad." statements above. I think soft_offline_page() is a candidate
> for a local fix because mm/memory-failure.c already has a significant
> amount of page-type specific knowledge. So teaching it "yes" for
> MEMORY_DEVICE_PRIVATE-ZONE_DEVICE and "no" for other ZONE_DEVICE seems
> ok to me.

I believe we do not want to teach _every_ pfn walker about zone device
pages. This would be quite error prone. Especially when a missig check
could lead to a silently broken data or BUG_ON with debugging enabled
(which is not the case for many production users). Or are we talking
about different bugs here?
-- 
Michal Hocko
SUSE Labs