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[195.135.220.15]) by mx.google.com with ESMTPS id k59si4737684edc.187.2019.02.13.06.23.09 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 13 Feb 2019 06:23:09 -0800 (PST) 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 CE619B120; Wed, 13 Feb 2019 14:23:08 +0000 (UTC) Date: Wed, 13 Feb 2019 15:23:08 +0100 From: Michal Hocko To: Robin Murphy Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: Fix __dump_page() for poisoned pages Message-ID: <20190213142308.GQ4525@dhcp22.suse.cz> References: 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 13-02-19 13:40:49, Robin Murphy wrote: > Evaluating page_mapping() on a poisoned page ends up dereferencing junk > and making PF_POISONED_CHECK() considerably crashier than intended. Fix > that by not inspecting the mapping until we've determined that it's > likely to be valid. Has this ever triggered? I am mainly asking because there is no usage of mapping so I would expect that the compiler wouldn't really call page_mapping until it is really used. > Fixes: 1c6fb1d89e73 ("mm: print more information about mapping in __dump_page") > Signed-off-by: Robin Murphy > --- > mm/debug.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/debug.c b/mm/debug.c > index 0abb987dad9b..1611cf00a137 100644 > --- a/mm/debug.c > +++ b/mm/debug.c > @@ -44,7 +44,7 @@ const struct trace_print_flags vmaflag_names[] = { > > void __dump_page(struct page *page, const char *reason) > { > - struct address_space *mapping = page_mapping(page); > + struct address_space *mapping; > bool page_poisoned = PagePoisoned(page); > int mapcount; > > @@ -58,6 +58,8 @@ void __dump_page(struct page *page, const char *reason) > goto hex_only; > } > > + mapping = page_mapping(page); > + > /* > * Avoid VM_BUG_ON() in page_mapcount(). > * page->_mapcount space in struct page is used by sl[aou]b pages to > -- > 2.20.1.dirty > -- Michal Hocko SUSE Labs