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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 6F852C5519F for ; Wed, 18 Nov 2020 13:58:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0A93B2078D for ; Wed, 18 Nov 2020 13:58:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726503AbgKRN5g (ORCPT ); Wed, 18 Nov 2020 08:57:36 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:57889 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725613AbgKRN5g (ORCPT ); Wed, 18 Nov 2020 08:57:36 -0500 Received: from fsav110.sakura.ne.jp (fsav110.sakura.ne.jp [27.133.134.237]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 0AIDv8Au020864; Wed, 18 Nov 2020 22:57:08 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav110.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav110.sakura.ne.jp); Wed, 18 Nov 2020 22:57:08 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav110.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 0AIDv8Pa020860 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Wed, 18 Nov 2020 22:57:08 +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> <6933e938-f219-5e13-aee6-fe4de87eb43e@i-love.sakura.ne.jp> Message-ID: <81ab0ffd-6e80-c96c-053a-b1b4fe8694c1@i-love.sakura.ne.jp> Date: Wed, 18 Nov 2020 22:57:08 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.3 MIME-Version: 1.0 In-Reply-To: <6933e938-f219-5e13-aee6-fe4de87eb43e@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, do you have a plan to make this problem actionable? On 2020/10/18 22:02, Tetsuo Handa wrote: > 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(-)