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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 B493CC4363D for ; Fri, 2 Oct 2020 12:36:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 601D920719 for ; Fri, 2 Oct 2020 12:36:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="J2MYhD18" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387749AbgJBMgJ (ORCPT ); Fri, 2 Oct 2020 08:36:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37038 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725964AbgJBMgJ (ORCPT ); Fri, 2 Oct 2020 08:36:09 -0400 Received: from mail-qt1-x82a.google.com (mail-qt1-x82a.google.com [IPv6:2607:f8b0:4864:20::82a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C9F3BC0613D0 for ; Fri, 2 Oct 2020 05:36:08 -0700 (PDT) Received: by mail-qt1-x82a.google.com with SMTP id m9so347182qth.7 for ; Fri, 02 Oct 2020 05:36:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=Qte7dDEik/LGw+83souKDg7C3zKSP9QwGh1sa25ffbQ=; b=J2MYhD18E1gMXfoIFxude3BGmvj2VTNsUpjX5LmfGwJiRpu8SpLZxZ8Sc+vobz+DAE 7vnN8ngt6SiUtI+qy26qCnshsZXzrFKhOp36bwWAEVaqoNQq8NHjRmYzX8lzpFXZLopl eUVeRx+LuxdAz7R1MjNNb7VivDs1xAMsFHEW0khGZbg33Fuamw83EfcdoRDbXXp5BknE 7rmB2T29oD50BMjyNEJVzM8O0fSR+FtRPBa7LYaAJVN0nwotjhixVDy3BR8qLEdEzllZ 7juJTACbHwe2uilvlKf1msb7APGtN3Nc9wxYk7PTV1cx53jxJjfw8sFjGfoglhiMSlQI OpFQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=Qte7dDEik/LGw+83souKDg7C3zKSP9QwGh1sa25ffbQ=; b=hskyHqIugGkMDyUrKDQSG8Dly6AQc92G2iY3GUdsH+vwPhz9dqn9HQdtQ52VYnR0Lb rDFLJRZoN2OLSdYfbjeepMsoOA6THqAhslKlN89+M3cFc/PKZnY6VukOjUyjpskStuQ1 qPcBvP++8xGVxIDPjhMtwC/brWgQD1fTmIaQ/uWju1e080NX6cNrrlCeb8NzLbdT8Lp7 +i5nFfCzwRZFi9K03cv+gUov9ON1dC62mTIUqRsKQvi8aa71J8F42BpircLPoV5esVMM ARzcH0D3qwWHwK8MPaGYKW7IIuIgl1esS9OB1q9D2d7n2/KDaDWD0DiBdfaYeV8GZbl8 cwYg== X-Gm-Message-State: AOAM533tiYs4AOrjH1vbWcQ03jsJ2wT+FUBcdwlM19A9rCVNbFjGoUBI ggCMV3on70MjTg1KLGWFQ58= X-Google-Smtp-Source: ABdhPJxxNm3Rg688Jf0S4RH8et/jCNOzqOnd85PzttsW95poYC6dttpsKXFGKEZRSSJz+YrA3EkLoQ== X-Received: by 2002:ac8:7145:: with SMTP id h5mr2121246qtp.110.1601642167129; Fri, 02 Oct 2020 05:36:07 -0700 (PDT) Received: from auth2-smtp.messagingengine.com (auth2-smtp.messagingengine.com. [66.111.4.228]) by smtp.gmail.com with ESMTPSA id 5sm917641qkj.135.2020.10.02.05.36.05 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 02 Oct 2020 05:36:06 -0700 (PDT) Received: from compute5.internal (compute5.nyi.internal [10.202.2.45]) by mailauth.nyi.internal (Postfix) with ESMTP id 31A1C27C0054; Fri, 2 Oct 2020 08:36:05 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute5.internal (MEProxy); Fri, 02 Oct 2020 08:36:05 -0400 X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedujedrfeeigdehvdcutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenuc fjughrpeffhffvuffkfhggtggujgesthdtredttddtvdenucfhrhhomhepuehoqhhunhcu hfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrihhlrdgtohhmqeenucggtffrrghtth gvrhhnpedvleeigedugfegveejhfejveeuveeiteejieekvdfgjeefudehfefhgfegvdeg jeenucfkphephedvrdduheehrdduuddurdejudenucevlhhushhtvghrufhiiigvpedtne curfgrrhgrmhepmhgrihhlfhhrohhmpegsohhquhhnodhmvghsmhhtphgruhhthhhpvghr shhonhgrlhhithihqdeiledvgeehtdeigedqudejjeekheehhedvqdgsohhquhhnrdhfvg hngheppehgmhgrihhlrdgtohhmsehfihigmhgvrdhnrghmvg X-ME-Proxy: Received: from localhost (unknown [52.155.111.71]) by mail.messagingengine.com (Postfix) with ESMTPA id EE06C3280063; Fri, 2 Oct 2020 08:36:03 -0400 (EDT) Date: Fri, 2 Oct 2020 20:36:02 +0800 From: Boqun Feng To: Peter Zijlstra Cc: g@hirez.programming.kicks-ass.net, Qian Cai , Waiman Long , Ingo Molnar , Will Deacon , linux-kernel@vger.kernel.org Subject: Re: lockdep null-ptr-deref Message-ID: <20201002123602.GE17810@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> References: <5fd046115645daa00f8841f5467da4c4d960ca92.camel@redhat.com> <20200929230823.GC17810@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> <20200930091610.GV2628@hirez.programming.kicks-ass.net> <20200930094937.GE2651@hirez.programming.kicks-ass.net> <20200930121818.GD17810@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> <20200930190228.GL2611@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200930190228.GL2611@hirez.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 30, 2020 at 09:02:28PM +0200, Peter Zijlstra wrote: > On Wed, Sep 30, 2020 at 08:18:18PM +0800, Boqun Feng wrote: > > > For one thing, I do think that LOCK_READ_USED trace is helpful for > > better reporting, because if there is a read lock in the dependency path > > which causes the deadlock, it's better to have the LOCK_READ_USED trace > > to know at least the initial READ usage. For example, if we have > > > > void f1(...) > > { > > write_lock(&A); > > spin_lock(&C); > > // A -> C > > ... > > } > > > > void g(...) > > { > > read_lock(&A); > > ... > > } > > void f2(...) > > { > > spin_lock(&B); > > g(...); > > // B -> A > > } > > > > void f3(...) { > > spin_lock(&C); > > spin_lock(&B); > > // C -> B, trigger lockdep splat > > } > > > > when lockdep reports the deadlock (at the time f3() is called), it will > > be useful if we have a trace like: > > > > INITIAL READ usage at: > > g+0x.../0x... > > f2+0x.../0x... > > > > Thoughts? > > Wouldn't that also be in LOCK_ENABLED_*_READ ? > But what if f2() is called with interrupt disabled? Or f2() disables interrupt inside the function, like: void f2(...) { local_irq_disable(); spin_lock(&B); g(...); ... local_irq_enable(); } In this case, there wouldn't be any LOCK_ENABLED_*_READ usage for rwlock_t A. As a result, we won't see it in the lockdep splat. Regards, Boqun > That is, with PROVE_LOCKING on, the initial usage is bound to set more > states, except for !check||trylock usage, and those aren't really all > that interesting.