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=-8.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 79417C433DF for ; Sun, 18 Oct 2020 13:03:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3E20D21655 for ; Sun, 18 Oct 2020 13:03:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726600AbgJRNDA (ORCPT ); Sun, 18 Oct 2020 09:03:00 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:53657 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725837AbgJRNC7 (ORCPT ); Sun, 18 Oct 2020 09:02:59 -0400 Received: from fsav102.sakura.ne.jp (fsav102.sakura.ne.jp [27.133.134.229]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 09ID2Uma037582; Sun, 18 Oct 2020 22:02:30 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav102.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav102.sakura.ne.jp); Sun, 18 Oct 2020 22:02:30 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav102.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 09ID2M1L037395 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Sun, 18 Oct 2020 22:02:30 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH v3] lockdep: Allow tuning tracing capacity constants. From: Tetsuo Handa To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Andrew Morton , linux-kernel@vger.kernel.org, Dmitry Vyukov , Linus Torvalds References: <1595640639-9310-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <384ce711-25c5-553b-8d22-965847132fbd@i-love.sakura.ne.jp> <0eb519fa-e77b-b655-724a-4e9eecc64626@i-love.sakura.ne.jp> Message-ID: <6933e938-f219-5e13-aee6-fe4de87eb43e@i-love.sakura.ne.jp> Date: Sun, 18 Oct 2020 22:02:19 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 MIME-Version: 1.0 In-Reply-To: <0eb519fa-e77b-b655-724a-4e9eecc64626@i-love.sakura.ne.jp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter, what do you think? Can we apply this patch? A potential for-now workaround for syzkaller would be to allow syzkaller not to encounter the BUG: message (by masking BUG: message on the kernel side) when hitting these limits, for continue testing until the kernel crashes (due to other bugs like UAF) would be to some degree useful. On 2020/10/10 21:58, Tetsuo Handa wrote: > Since syzkaller continues various test cases until the kernel crashes, > syzkaller tends to examine more locking dependencies than normal systems. > As a result, syzbot is reporting that the fuzz testing was terminated > due to hitting upper limits lockdep can track [1] [2] [3]. > > Peter Zijlstra does not want to allow tuning these limits via kernel > config options, for such change discourages thinking. But currently we > are not actionable, for lockdep does not report the culprit for hitting > these limits [4]. > > Therefore, I propose this patch again, with a caveat that this patch is > expected to be reverted after lockdep becomes capable of reporting the > culprit, for I consider that "postpone fixing lock related problems in > existing code" is less painful than "not detecting lock related problems > introduced by new patches". > > [1] https://syzkaller.appspot.com/bug?id=3d97ba93fb3566000c1c59691ea427370d33ea1b > [2] https://syzkaller.appspot.com/bug?id=381cb436fe60dc03d7fd2a092b46d7f09542a72a > [3] https://syzkaller.appspot.com/bug?id=a588183ac34c1437fc0785e8f220e88282e5a29f > [4] https://lkml.kernel.org/r/CACT4Y+agTiEF-1i9LbAgp-q_02oYF0kAPZGAAJ==-wx2Xh7xzQ@mail.gmail.com > > Reported-by: syzbot > Reported-by: syzbot > Reported-by: syzbot > Signed-off-by: Tetsuo Handa > Acked-by: Dmitry Vyukov > --- > kernel/locking/lockdep.c | 2 +- > kernel/locking/lockdep_internals.h | 8 +++--- > lib/Kconfig.debug | 40 ++++++++++++++++++++++++++++++ > 3 files changed, 45 insertions(+), 5 deletions(-)