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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 D8D98C33CAD for ; Mon, 13 Jan 2020 13:09:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ACB892081E for ; Mon, 13 Jan 2020 13:09:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578920999; bh=gyDnNoKTZ22DZEKM3QxIzE68ZWjkRDMYhM7ep5kP+vY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=bAAS5NbfHE8g7xMbr1+RzEjsZZkaeeEYlm7vjF3qTN9nc3USBk0BkUA+0+o+hPpo5 9jYSMzVXgzYt4FCicyvIUGuuvrZHNwex53QC1ueL14sS2x+07DdJoytiBIe5+e3OFs IHABecXv7JorrYpCsX0X4nGLwTBgcdPde3Ax8L9I= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728512AbgAMNJ6 (ORCPT ); Mon, 13 Jan 2020 08:09:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:50942 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726593AbgAMNJ6 (ORCPT ); Mon, 13 Jan 2020 08:09:58 -0500 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3E13D2081E; Mon, 13 Jan 2020 13:09:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578920997; bh=gyDnNoKTZ22DZEKM3QxIzE68ZWjkRDMYhM7ep5kP+vY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=QxahobyLvunSkXeHTuFOBUvUoh6nvqy37qLTmDjYC57O8ERCuJYtmkCunKXQ7Dg/r +SWipHnGylfCg4ughxj3i++/eQMiH2JGQ9FSxN/7zq1QMEVVOeVoYh4AB/Pv8DDMVD I+6BKtXViF8PCn+nhNa1aApR7pS6mcgh95T01PmQ= Date: Mon, 13 Jan 2020 22:09:53 +0900 From: Masami Hiramatsu To: Masami Hiramatsu Cc: Joel Fernandes , Ingo Molnar , Anders Roxell , paulmck@kernel.org, "Naveen N . Rao" , Anil S Keshavamurthy , David Miller , Linux Kernel Mailing List Subject: Re: [PATCH -tip V2 0/2] kprobes: Fix RCU warning and cleanup Message-Id: <20200113220953.dccefd4846d004ee5a5b3295@kernel.org> In-Reply-To: <20200113121640.bfab48c105dae9b1918c2d82@kernel.org> References: <157535316659.16485.11817291759382261088.stgit@devnote2> <20191221035541.69fc05613351b8dabd6e1a44@kernel.org> <20200107211535.233e7ff396f867ee1348178b@kernel.org> <20200110211438.GE128013@google.com> <20200111083507.c32b85b1d47aa69928de530b@kernel.org> <20200112020537.GJ128013@google.com> <20200113121640.bfab48c105dae9b1918c2d82@kernel.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Joel, On Mon, 13 Jan 2020 12:16:40 +0900 Masami Hiramatsu wrote: > > > > > > > > Hi Masami, > > > > > > > > I believe I had commented before that I don't agree with this patch: > > > > https://lore.kernel.org/lkml/157535318870.16485.6366477974356032624.stgit@devnote2/ > > > > > > > > The rationale you used is to replace RCU-api with non-RCU api just to avoid > > > > warnings. I think a better approach is to use RCU api and pass the optional > > > > expression to silence the false-positive warnings by informing the RCU API > > > > about the fact that locks are held (similar to what we do for > > > > rcu_dereference_protected()). The RCU API will do additional checking > > > > (such as making sure preemption is disabled for safe RCU usage etc) as well. > > > > > > Yes, that is what I did in [1/2] for get_kprobe(). > > > Let me clarify the RCU list usage in [2/2]. > > > > > > With the careful check, other list traversals never be done in non-sleepable > > > context, those are always runs with kprobe_mutex held. > > > If I correctly understand the Documentation/RCU/listRCU.rst, we should/can use > > > non-RCU api for those cases, or do I miss something? > > > > Yes, that is fine. However personally I prefer not to mix usage of > > list_for_each_entry_rcu() and list_for_each_entry() on the same pointer > > (kprobe_table). I think it is more confusing and error prone. Just use > > list_for_each_entry_rcu() everywhere and pass the appropriate lockdep > > expression, instead of calling lockdep_assert_held() independently. Is this > > not doable? > > Hmm, but isn't it more confusing that user just take a mutex but > no rcu_read_lock() with list_for_each_entry_rcu()? In that case, > sometimes it might sleep inside list_for_each_entry_rcu(), I thought > that might be more confusing mind model for users... I meant, do we always need to do something like below? { mutex_lock(&lock); list_for_each_entry_rcu(list, ..., lockdep_is_held(&lock)) { ... } mutex_unlock(&lock); } BTW, I found another problem on this policy, since we don't have list_for_each_*_safe() equivalents for RCU, we can not do a safe loop on it. Should we call a find function for each time? Thank you, -- Masami Hiramatsu