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Date:   Wed, 26 Jun 2019 08:59:35 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Alastair D'Silva <alastair@d-silva.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Pavel Tatashin <pasha.tatashin@oracle.com>,
        Oscar Salvador <osalvador@suse.de>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Baoquan He <bhe@redhat.com>, Qian Cai <cai@lca.pw>,
        Logan Gunthorpe <logang@deltatee.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2 2/3] mm: don't hide potentially null memmap pointer in
 sparse_remove_one_section
Message-ID: <20190626065935.GL17798@dhcp22.suse.cz>
References: <20190626061124.16013-1-alastair@au1.ibm.com>
 <20190626061124.16013-3-alastair@au1.ibm.com>
 <20190626062344.GG17798@dhcp22.suse.cz>
 <edac179f0626a6e0bd91922d876934abf1b9bb19.camel@d-silva.org>
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On Wed 26-06-19 16:30:55, Alastair D'Silva wrote:
> On Wed, 2019-06-26 at 08:23 +0200, Michal Hocko wrote:
> > On Wed 26-06-19 16:11:22, Alastair D'Silva wrote:
> > > From: Alastair D'Silva <alastair@d-silva.org>
> > > 
> > > By adding offset to memmap before passing it in to
> > > clear_hwpoisoned_pages,
> > > we hide a potentially null memmap from the null check inside
> > > clear_hwpoisoned_pages.
> > > 
> > > This patch passes the offset to clear_hwpoisoned_pages instead,
> > > allowing
> > > memmap to successfully peform it's null check.
> > 
> > Same issue with the changelog as the previous patch (missing WHY).
> > 
> 
> The first paragraph explains what the problem is with the existing code
> (same applies to 1/3 too).

Under what conditions that happens? Is this a theoretical problem or can
you hit this by a (buggy) code? Please be much more specific.

-- 
Michal Hocko
SUSE Labs