From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.3 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AB8A4C432C3 for ; Thu, 21 Nov 2019 20:13:27 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6657820672 for ; Thu, 21 Nov 2019 20:13:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Ivm+77kB" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6657820672 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 14B256B037A; Thu, 21 Nov 2019 15:13:27 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0FCB06B037B; Thu, 21 Nov 2019 15:13:27 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 012566B037C; Thu, 21 Nov 2019 15:13:26 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0184.hostedemail.com [216.40.44.184]) by kanga.kvack.org (Postfix) with ESMTP id E065E6B037A for ; Thu, 21 Nov 2019 15:13:26 -0500 (EST) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id 7958A2C89 for ; Thu, 21 Nov 2019 20:13:26 +0000 (UTC) X-FDA: 76181384412.11.toys15_1dfc05c50614b X-HE-Tag: toys15_1dfc05c50614b X-Filterd-Recvd-Size: 5892 Received: from mail-qk1-f195.google.com (mail-qk1-f195.google.com [209.85.222.195]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Thu, 21 Nov 2019 20:13:25 +0000 (UTC) Received: by mail-qk1-f195.google.com with SMTP id o17so4257663qko.6 for ; Thu, 21 Nov 2019 12:13:25 -0800 (PST) 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=L7kYoMVgzXrrlMqhKt4mkkLjEcR7Iirse1ze91WZ2es=; b=Ivm+77kBP6dszmfwrcPYZpVNUzPEQ41aylYiP4xCZ5ljESqvBEFVvKTD2AEwmdOsL4 14ZKZEuU2lOHuPag2Cv7szEQeCTGabe+e3UHltjZORlPWrWo1hgPvhm2w3kHeP6nb+gi o1TXg3NKP1VYP+fadqTqmMG9+StLeCRDU2dwzw91Rngm8de9h5b01xCy8fDo3OzvdGKc 7sHbPWh3oF83aJ8I6i1tNam8zl1lgPg1cwehgcJ5YHq3oa13BgDC4vjo5ndPqn8nrlOU 8scXT9s6A7/UyWL+yqZhVg+Lgl/0/1oPsHxN3/uHlqPYwTVN9cZ3becP/n2dC7RRMmDY zfRA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=L7kYoMVgzXrrlMqhKt4mkkLjEcR7Iirse1ze91WZ2es=; b=nQR2CSRTG85NDFJdMCjKJdMrN4MlsrJ3psF0v43slFUwb5xufqaIGJdrxR/JZvcXmz X7XeNNblULRZ9JQq1B8VRupFDDHE5fOHUG1zAR8NOasIjGO5HkeymnHuFSiwZClQpovu HgN8y/XyFuCeCxBCeDDgGb8cXwZXAfKUB/DLqIM568T1A9bBOzmWQn88g4d4yLb6HVUa keStbETjL37aUj5SZIHnQxA5XS6TaKTSO8lriW7Yk15PhiOEmtVrJ4jXaN8PRQDntSjP dUasws8hG3KMXYlKLHlHLjyve3urdh+SkUWlo6jdKbyd6sAT9X/TSZ5c16S5+ggKHHYC 7DVA== X-Gm-Message-State: APjAAAVhSCSONO0mjVRuZA7qnXcFSZ4oGH2rPTAnrpL06ddYvF0g1Lu/ jcbXoLNUD3pJtUJxIb4HuVU9Uxq5w6c933bj7lWp1w== X-Google-Smtp-Source: APXvYqwLvEyx2OYuY5lEgxSfNmvYOcfePTvN/jgculMxRa6kgYzB7S5fAyaH0IZgpTPo0C5Pc2siam/z5wfKTiRPtpY= X-Received: by 2002:a05:620a:14b9:: with SMTP id x25mr1608539qkj.8.1574367204856; Thu, 21 Nov 2019 12:13:24 -0800 (PST) MIME-Version: 1.0 References: <0000000000006e31980579315914@google.com> <000000000000a6993c0597cc8375@google.com> In-Reply-To: From: Dmitry Vyukov Date: Thu, 21 Nov 2019 21:13:12 +0100 Message-ID: Subject: Re: INFO: task hung in __do_page_fault (2) To: Andy Lutomirski Cc: syzbot , Arnaldo Carvalho de Melo , Andrew Morton , Arnd Bergmann , Jonathan Corbet , "Eric W. Biederman" , Kees Cook , "open list:DOCUMENTATION" , LKML , Linux-MM , Dominik Brodowski , "Luis R. Rodriguez" , Ingo Molnar , Peter Zijlstra , Sudip Mukherjee , syzkaller-bugs , Linus Torvalds 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 Thu, Nov 21, 2019 at 7:01 PM Andy Lutomirski wrote: > > On Wed, Nov 20, 2019 at 11:52 AM syzbot > wrote: > > > > syzbot has bisected this bug to: > > > > commit 0161028b7c8aebef64194d3d73e43bc3b53b5c66 > > Author: Andy Lutomirski > > Date: Mon May 9 22:48:51 2016 +0000 > > > > perf/core: Change the default paranoia level to 2 > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15910e86e00000 > > start commit: 18d0eae3 Merge tag 'char-misc-4.20-rc1' of git://git.kerne.. > > git tree: upstream > > final crash: https://syzkaller.appspot.com/x/report.txt?x=17910e86e00000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=13910e86e00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=342f43de913c81b9 > > dashboard link: https://syzkaller.appspot.com/bug?extid=6b074f741adbd93d2df5 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12482713400000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=158fd4a3400000 > > > > Reported-by: syzbot+6b074f741adbd93d2df5@syzkaller.appspotmail.com > > Fixes: 0161028b7c8a ("perf/core: Change the default paranoia level to 2") > > > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection > > Hi syzbot- > > I'm not quite sure how to tell you this in syzbotese, but I'm pretty > sure you've bisected this wrong. The blamed patch makes no sense. Hi Andy, Three is no way to tell syzbot about this, it does not have any way to use this information. You can tell this to other recipients, though, and for the record on the bug report email thread. For this you can use any free form. But what makes you think this is wrong? >From everything I see this looks like amazingly precise bisection. The reproducer contains perf_event_open which seems to cause the hang (there is a number of reports where perf_event_open hangs kernel dead IIRC) _and_ it contains setresuid. Which makes good match for "perf/core: Change the default paranoia level to 2" (for unpriv users). The bisection log also looks perfectly correct to me: no unrelated kernel bugs were hit along the way; the crash was always reproduced 100% reliably in all 10 runs; nothing else suspicious. I can totally imagine that your patch unmasked some latent bug, but it's not 100% obvious to me and in either case syzbot did the job as well as a robot could possibly do.