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[217.140.110.172]) by mx.google.com with ESMTP id k41si12576206edb.152.2019.07.26.08.57.38 for ; Fri, 26 Jul 2019 08:57:38 -0700 (PDT) Received-SPF: pass (google.com: domain of catalin.marinas@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: domain of catalin.marinas@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=catalin.marinas@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4C6C3152D; Fri, 26 Jul 2019 08:57:37 -0700 (PDT) Received: from e109758.arm.com (unknown [10.1.39.157]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 50BC73F71F; Fri, 26 Jul 2019 08:57:35 -0700 (PDT) Date: Fri, 26 Jul 2019 16:57:32 +0100 From: Catalin Marinas To: Dmitry Vyukov Cc: syzbot , alexandre.belloni@free-electrons.com, LKML , Linux-MM , nicolas.ferre@atmel.com, Rob Herring , sre@kernel.org, syzkaller-bugs Subject: Re: memory leak in vq_meta_prefetch Message-ID: <20190726155732.GA30211@e109758.arm.com> References: <00000000000052ad6b058e722ba4@google.com> <20190726130013.GC2368@arrakis.emea.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.2 (2019-01-07) 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 Fri, Jul 26, 2019 at 05:20:55PM +0200, Dmitry Vyukov wrote: > On Fri, Jul 26, 2019 at 3:00 PM Catalin Marinas wrote: > > On Wed, Jul 24, 2019 at 12:18:07PM -0700, syzbot wrote: > > > syzbot found the following crash on: > > > > > > HEAD commit: c6dd78fc Merge branch 'x86-urgent-for-linus' of git://git... > > > git tree: upstream > > > console output: https://syzkaller.appspot.com/x/log.txt?x=15fffef4600000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=8de7d700ea5ac607 > > > dashboard link: https://syzkaller.appspot.com/bug?extid=a871c1e6ea00685e73d7 > > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=127b0334600000 > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12609e94600000 > > > > > > The bug was bisected to: > > > > > > commit 0e5f7d0b39e1f184dc25e3adb580c79e85332167 > > > Author: Nicolas Ferre > > > Date: Wed Mar 16 13:19:49 2016 +0000 > > > > > > ARM: dts: at91: shdwc binding: add new shutdown controller documentation > > > > That's another wrong commit identification (a documentation patch should > > not cause a memory leak). > > > > I don't really think kmemleak, with its relatively high rate of false > > positives, is suitable for automated testing like syzbot. You could > > Do you mean automated testing in general, or bisection only? > The wrong commit identification is related to bisection only, but you > generalized it to automated testing in general. So which exactly you > mean? I probably meant both. In terms of automated testing and reporting, if the false positives rate is high, people start ignoring the reports. So it requires some human checking first (or make the tool more robust). W.r.t. bisection, the false negatives (rather than positives) will cause the tool to miss the problematic commit and misreport. I'm not sure you can make the reporting deterministic on successive runs given that you changed the kernel HEAD (for bisection). But it may get better if you have a "stopscan" kmemleak option which freezes the machine during scanning (it has been discussed in the past but I really struggle to find time to work on it; any help appreciated ;)). -- Catalin