linux-kernel - Re: [PATCH v1 3/7] mm: rename and move page_is

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Date:   Wed, 5 May 2021 15:13:11 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        Roman Gushchin <guro@...com>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Steven Price <steven.price@....com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Aili Yao <yaoaili@...gsoft.com>, Jiri Bohac <jbohac@...e.cz>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-hyperv@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 3/7] mm: rename and move page_is_poisoned()

On Thu 29-04-21 14:25:15, David Hildenbrand wrote:
> Commit d3378e86d182 ("mm/gup: check page posion status for coredump.")
> introduced page_is_poisoned(), however, v5 [1] of the patch used
> "page_is_hwpoison()" and something went wrong while upstreaming. Rename the
> function and move it to page-flags.h, from where it can be used in other
> -- kcore -- context.
> 
> Move the comment to the place where it belongs and simplify.
> 
> [1] https://lkml.kernel.org/r/20210322193318.377c9ce9@alex-virtual-machine
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

I do agree that being explicit about hwpoison is much better. Poisoned
page can be also an unitialized one and I believe this is the reason why
you are bringing that up.

But you've made me look at d3378e86d182 and I am wondering whether this
is really a valid patch. First of all it can leak a reference count
AFAICS. Moreover it doesn't really fix anything because the page can be
marked hwpoison right after the check is done. I do not think the race
is feasible to be closed. So shouldn't we rather revert it?

-- 
Michal Hocko
SUSE Labs