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[195.135.220.15]) by mx.google.com with ESMTPS id la8si2091353ejb.359.2019.06.25.23.59.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 25 Jun 2019 23:59:38 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 94530AC83; Wed, 26 Jun 2019 06:59:38 +0000 (UTC) Date: Wed, 26 Jun 2019 08:59:35 +0200 From: Michal Hocko To: Alastair D'Silva Cc: Greg Kroah-Hartman , "Rafael J. Wysocki" , Andrew Morton , Pavel Tatashin , Oscar Salvador , Mike Rapoport , Baoquan He , Qian Cai , Logan Gunthorpe , 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > > > > > > 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