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=-2.2 required=3.0 tests=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 634A7C74A35 for ; Wed, 10 Jul 2019 18:36:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 42BCF20651 for ; Wed, 10 Jul 2019 18:36:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728140AbfGJSgp convert rfc822-to-8bit (ORCPT ); Wed, 10 Jul 2019 14:36:45 -0400 Received: from mail-pl1-f196.google.com ([209.85.214.196]:36683 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727193AbfGJSgo (ORCPT ); Wed, 10 Jul 2019 14:36:44 -0400 Received: by mail-pl1-f196.google.com with SMTP id k8so1652873plt.3 for ; Wed, 10 Jul 2019 11:36:44 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=A8Qs53e8oL8Rit9Ihe8NcNOpmThh1DKFAspTMJKydW0=; b=mYLzaaYbAWrDMQQ3ZnHI7uD5LPxxBroLPEubf2g5M7C1bPK/FjbuJgRoJXVrxU2ipA O01mBdDRJ1wN3Y7H0WyQcGt9TDinPPv4d+gs0ezouLdb6wOywtIa7AzqoO8QTzuqWOif k+8YWRFVLgZpU2WcaVO+ZC1qRIYl9yNWyEixc9QSx1Y5vdZLX8qESVAlWAQt3/epsDlb TrYNDL9Ac7MrTRMtz6kmeAAmcovor741Yrm4QgPrr7IB9q0fdA9xQa6L0xUzVWXMqytN LonPqgSRbHVdhucuedvXrRQ94RpWh8sdyQjuzGwROGcooCi2zGX9HrmhdbnxXNWMemQ0 Godw== X-Gm-Message-State: APjAAAXuPgpOk5p7S0Argb6d1byuOT4NDCSulY5C7WM/uIY0b1FET1P1 8YNqZhCIgHN4NKdPftMgTvG4pzQV X-Google-Smtp-Source: APXvYqw+rVs6cOCxom0649D34DZC/c0A50KHyFAbjBCsjrTXj5njyXdTZWSdMsPCSOFN30O1RgIujQ== X-Received: by 2002:a17:902:e383:: with SMTP id ch3mr40236752plb.23.1562783803956; Wed, 10 Jul 2019 11:36:43 -0700 (PDT) Received: from ?IPv6:2620:15c:2c1:200:fb9c:664d:d2ad:c9b5? ([2620:15c:2c1:200:fb9c:664d:d2ad:c9b5]) by smtp.gmail.com with ESMTPSA id q144sm2925710pfc.103.2019.07.10.11.36.42 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Jul 2019 11:36:43 -0700 (PDT) Subject: Re: BUG: MAX_STACK_TRACE_ENTRIES too low! (2) To: Peter Zijlstra , Ingo Molnar , Will Deacon , linux-kernel@vger.kernel.org, syzbot , syzkaller-bugs@googlegroups.com References: <00000000000089a718058556e1d8@google.com> <20190710053030.GB2152@sol.localdomain> <20190710170057.GB801@sol.localdomain> <20190710172123.GC801@sol.localdomain> <20190710180242.GA193819@gmail.com> From: Bart Van Assche Message-ID: Date: Wed, 10 Jul 2019 11:36:41 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190710180242.GA193819@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/10/19 11:02 AM, Eric Biggers wrote: > I already mentioned that io_uring triggers it too. > > Those are just 2 cases that syzbot happened to generate reproducers for. I > expect there are many others too, since many places in the kernel allocate > workqueues. AFAICS most are placed in static or global variables which avoids > this issue, but there are still many cases where a workqueue is owned by some > dynamic structure that can have a much shorter lifetime. > > You can also check the other syzbot reports that look similar > (https://lore.kernel.org/lkml/20190710055838.GC2152@sol.localdomain/). > Two of them have C reproducers too. As you may know lockdep cannot use dynamic memory allocation because doing so would introduce a circular dependency between lockdep and the memory allocator. Hence the fixed size arrays in the lockdep code. Additionally, as far as I know lockdep works fine for human kernel developers and only syzbot runs code that triggers the lockdep limits. So I think it's up to the syzbot authors to come up with a solution. I mean another solution than finger pointing at kernel developers. Bart.