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[209.85.220.65]) by mx.google.com with SMTPS id d21sor37397978ioc.57.2019.07.26.09.26.20 for (Google Transport Security); Fri, 26 Jul 2019 09:26:20 -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=oSxV5e5b; 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=49yfm4zari4iNgyc4c8iUnGnNiF8H5iDhklR2GX7QUY=; b=oSxV5e5bNKAEOl0HwhKJhFqS6oocpVP8oUntBD5al/WdfjqqJtsIfjWUwUDx29tEVj Ocox6SNSxTgTxci3S8uus+9f4v048jOPUOqwuyvdGpFBolmfQvjuixpWQTQ5t5g8nuwr Sy9w9ffMso7C/QX4f1ZEvHSPRs5SJNYv6cimfjMXpAyHuG6KjU7Rsm1uupYDv1xHZZxm U9VXVqwxnRXp45lR+vyNSgiPcH8dTiR7z+dw7MCbH2Yt6OKPOLKCfrRN86ogxLxP1o2E CbNgCMUgLLBu374M3UiEjVmgk6BDWDqRqVAPodQaRsA6oqmCQhhul6kJGPCrPdH4BVfB 3cNg== X-Google-Smtp-Source: APXvYqyjf4GbmLPhL55X+s5p3TCQUBLJfRXVKJ2wZzfFHaTvxUziKKWb5psRA8Z3KyOrSCo3gRDt5OcQAS+5PqQqTdQ= X-Received: by 2002:a5d:80d6:: with SMTP id h22mr65658210ior.231.1564158379700; Fri, 26 Jul 2019 09:26:19 -0700 (PDT) MIME-Version: 1.0 References: <00000000000052ad6b058e722ba4@google.com> <20190726130013.GC2368@arrakis.emea.arm.com> <20190726155732.GA30211@e109758.arm.com> <20190726161530.GE2368@arrakis.emea.arm.com> In-Reply-To: <20190726161530.GE2368@arrakis.emea.arm.com> From: Dmitry Vyukov Date: Fri, 26 Jul 2019 18:26:08 +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 6:15 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). > [...] > > Do you have any data points wrt automated testing in general? This > > disagrees with what I see. > > I'm fine with automated testing in general. Just that automated > reporting for kmemleak could be improved a bit to reduce the false > positives (e.g. run it a few times to confirm that it is a real leak). I did a bunch of various external measures in syzkaller to improve kmemleak quality. As far as I see the current rate is close to 100% true positives. We already have 40 leaks (>50%) fixed. Though, kmemleak can be improved too (stop-the-world, etc what we discussed). That would make kmemleak directly usable e.g. during unit-testing, something that's badly needed for kernel. > Just to be clear, I'm not talking about syzbot in general, it's a great > tool, only about improving kmemleak reporting and bisecting.