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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 57D2AC33CB1 for ; Tue, 14 Jan 2020 08:43:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 28D72207FF for ; Tue, 14 Jan 2020 08:43:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="lGEURDl4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728799AbgANInq (ORCPT ); Tue, 14 Jan 2020 03:43:46 -0500 Received: from merlin.infradead.org ([205.233.59.134]:40930 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725904AbgANInp (ORCPT ); Tue, 14 Jan 2020 03:43:45 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=U3RF+wuU6+PT2BD7xbGzYkq6o+SbUI6E7+a+DjOKcEM=; b=lGEURDl402SmQX3dHrrkytLB2 qOPkT0b/UXb0MCSpM7PTMQfdOMJvDMfPYozEXcQAS6y2FZZXnOvgMjP+n3x7GPsP7RUyvstZUH1O1 lvbibsF4PfUM9wZutgYPdWYLZvpH9W5914PWT3bFKXgPwQRCcOaoA2SqO3E7c43vq29jlquyr3fbj KF/YnOiPXX8zsEkI9QyzzfE8aEihcGhZOzjMsu25fGQpW/zbBDD901nE0NNlRUEWTBZ9BKGYYSujD RdqqOlzC2L7kkclR0+4DeAXLeM0hl06rwgBN11YQ+ABzW/Mk9wR4TSPb2JiM9ZM02+2IucS1ZEBdq l9+SB1q2w==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1irHnT-0005FB-LE; Tue, 14 Jan 2020 08:43:35 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 81179304BDF; Tue, 14 Jan 2020 09:41:58 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 232F8201D41A2; Tue, 14 Jan 2020 09:43:34 +0100 (CET) Date: Tue, 14 Jan 2020 09:43:34 +0100 From: Peter Zijlstra To: Dmitry Vyukov Cc: syzbot , Ingo Molnar , Will Deacon , LKML , syzkaller-bugs , Thomas Gleixner Subject: Re: BUG: MAX_LOCKDEP_CHAINS too low! Message-ID: <20200114084334.GI2827@hirez.programming.kicks-ass.net> References: <0000000000007523a60576e80a47@google.com> <20180928070042.GF3439@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 09, 2020 at 11:59:25AM +0100, Dmitry Vyukov wrote: > Or are there some ID leaks in lockdep? syzbot has a bunch of very > simple reproducers for these bugs, so not really a maximally diverse > load. And I think I saw these bugs massively when testing just a > single subsystem too, e.g. netfilter. Can you share me one of the simple ones? A .c files I can run on my regular test box that should make it go *splat* ? Often in the past hitting these limits was the result of some particularly poor annotation. For instance, locks in per-cpu data used to trigger this, since static locks don't need explicit {mutex,spin_lock}_init() calls and instead use their (static) address. This worked fine for global state, but per-cpu is an exception, there it causes a nr_cpus explosion in lockdep state because you get nr_cpus different addresses. Now, we fixed that particular issue: 383776fa7527 ("locking/lockdep: Handle statically initialized PER_CPU locks properly") but maybe there's something else going on. Just blindly bumping the number without analysis of what exactly is happening is never a good idea.