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[209.85.220.65]) by mx.google.com with SMTPS id r11sor36149552ioh.122.2019.07.26.08.21.09 for (Google Transport Security); Fri, 26 Jul 2019 08:21:09 -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=N0w2rApM; 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=F9G1CH0Ps2FRcZ/NwMc7CwEB3cMwgOdfmNpmMO9HdoM=; b=N0w2rApMLkoaZxE6gBTrU8k8luxL61ZdCWczIF69GZlKQMFUb4lG2guayRg6yAIpbk H1X366pDlqnI3DIuEPp2eBW6njqlQnGw537yrxBAD3BJ8WtV/88SiHMNhsFBE5NfC8Mc 6pFDGGrtahrlAC+muBEsD3Uw/mU6kjLtiI4R5g3tYOUIQwjj+xGug574LijMJ9525yyM PBE6JWBDuqPjDFgkXCHTfNPmGyDCt/onMSaEIBQ8DSyYxWlpz9e/7Zj/YiwrwWq4N/JH c1tG2fhMhAiOJtHrldKpL6DVeLTIm6XxQznNCdMNS+EWp3QiFKDkpkNeDLme62XdCPgV PtnQ== X-Google-Smtp-Source: APXvYqzWkKaER3d1SoL4pM51luD5r76GIZCi5wBc/4zHT9xYg4/8N5PMzy6UISLqCi9oNf8Xd9jLBaT9T4dOYpBVyvo= X-Received: by 2002:a5d:80d6:: with SMTP id h22mr65334094ior.231.1564154468687; Fri, 26 Jul 2019 08:21:08 -0700 (PDT) MIME-Version: 1.0 References: <00000000000052ad6b058e722ba4@google.com> <20190726130013.GC2368@arrakis.emea.arm.com> In-Reply-To: <20190726130013.GC2368@arrakis.emea.arm.com> From: Dmitry Vyukov Date: Fri, 26 Jul 2019 17:20:55 +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 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 Hi Catalin, 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? > reduce the false positives if you add support for scanning in > stop_machine(). Otherwise, in order to avoid locking the kernel for long > periods, kmemleak runs concurrently with other threads (even on the > current CPU) and under high load, pointers are missed (e.g. they are in > CPU registers rather than stack).