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[209.85.220.65]) by mx.google.com with SMTPS id a3sor36461187ioh.83.2019.07.26.09.05.46 for (Google Transport Security); Fri, 26 Jul 2019 09:05:46 -0700 (PDT) Received-SPF: pass (google.com: domain of dvyukov@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b="K/SemTMC"; spf=pass (google.com: domain of dvyukov@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=dvyukov@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=AoOpJrER5lkg8Em3wVFNio3C8LuUFynD4kdmk02EVZ0=; b=K/SemTMCiXyHQbxfV2/uM8winVoyG6FtMvMdX/B+Oqq2d1DvUDoowKjgxlbhSDPVEP 6N2KrxCjCa3L6kPlOHoOmcyt4p29enh4lTg2fySZvfq2wqMET4gI9XXsxGYZQ30Zgxpx 1Yd6fx1meAwrU3ECP7TW7HHVeOujY4aD4OjAWxDNBjmUMU8gThZsy3oReR5/++8YoNjg 9YtuwFes1R2FIKfjGXpy8bFLIVBn75lR8c8VZYeGaDyXzPNEgxkWlL6wjU4v0Qch10d4 xXy75iwQ/8GTCO7xHgzprutgoPpUT5Cs21giNQHKN69g1Xz2CFHIezxUic9NvJFMkz/a yw1Q== X-Google-Smtp-Source: APXvYqx1DMdxq/O+3koIzpoMVm15SRd82G8zIAIH2kBNUwLkI3sjNquWgQypNmv9GFwq6RmdFU5SwnkJU44a6givHcA= X-Received: by 2002:a6b:4101:: with SMTP id n1mr61984828ioa.138.1564157145336; Fri, 26 Jul 2019 09:05:45 -0700 (PDT) MIME-Version: 1.0 References: <00000000000052ad6b058e722ba4@google.com> <20190726130013.GC2368@arrakis.emea.arm.com> <20190726155732.GA30211@e109758.arm.com> In-Reply-To: <20190726155732.GA30211@e109758.arm.com> From: Dmitry Vyukov Date: Fri, 26 Jul 2019 18:05:32 +0200 Message-ID: Subject: Re: memory leak in vq_meta_prefetch To: Catalin Marinas Cc: syzbot , alexandre.belloni@free-electrons.com, LKML , Linux-MM , nicolas.ferre@atmel.com, Rob Herring , sre@kernel.org, syzkaller-bugs Content-Type: text/plain; charset="UTF-8" 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 5:57 PM Catalin Marinas wrote: > > 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 ;)). Do you have any data points wrt automated testing in general? This disagrees with what I see. For bisection, I agree. Need to look at the data we got over the past days when it become enabled. But I suspect that, yes, false positives, flakes, and other true leaks can make it infeasible.