linux-kernel - Re: [PATCH v1] mm: Fix access of uninitialized memmaps in fs/proc/page.c

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Date:   Wed, 9 Oct 2019 13:24:24 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Qian Cai <cai@....pw>, Alexey Dobriyan <adobriyan@...il.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Toshiki Fukasawa <t-fukasawa@...jp.nec.com>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Anthony Yznaga <anthony.yznaga@...cle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Ira Weiny <ira.weiny@...el.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v1] mm: Fix access of uninitialized memmaps in
 fs/proc/page.c

On Wed 09-10-19 12:19:59, David Hildenbrand wrote:
[...]
> > pfn_to_online_page makes sense because offline pages are not really in a
> > defined state. This would be worth a patch of its own. I remember there
> 
> The issue is, once I check for pfn_to_online_page(), these functions
> can't handle ZONE_DEVICE at all anymore. Especially in regards to
> memory_failure() I don't think this is acceptable.

Could you be more specific please? I am not sure I am following.

> So while I
> (personally) only care about adding pfn_to_online_page() checks, the
> in-this-sense-fragile-subsection ZONE_DEVICE implementation requires me
> to introduce a temporary check for initialized memmaps.
> 
> > was a discussion about the uninitialized zone device memmaps. It would
> > be really good to summarize this discussion in the changelog and
> > conclude why the explicit check is really good and what were other
> > alternatives considered.
> 
> Yeah, I also expressed my feelings and the issues to be solved by
> ZONE_DEVICE people in https://lkml.org/lkml/2019/9/6/114. However, the
> discussion stalled and nobody really proposed a solution or followed up.

I will try to get back to that discussion but is there any technical
reason that prevents any conclusion or it is just stuck on a lack of
time of the participants?

-- 
Michal Hocko
SUSE Labs