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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C09E2C433EF for ; Tue, 12 Oct 2021 12:29:53 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2D99E610D1 for ; Tue, 12 Oct 2021 12:29:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 2D99E610D1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4HTFNb3K3Qz2yPn for ; Tue, 12 Oct 2021 23:29:51 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=198.145.29.99; helo=mail.kernel.org; envelope-from=srs0=yp9m=pa=goodmis.org=rostedt@kernel.org; receiver=) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4HTFN705rdz2xrq for ; Tue, 12 Oct 2021 23:29:26 +1100 (AEDT) Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (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 8122460E74; Tue, 12 Oct 2021 12:29:21 +0000 (UTC) Date: Tue, 12 Oct 2021 08:29:20 -0400 From: Steven Rostedt To: Miroslav Benes Subject: Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion Message-ID: <20211012082920.1f8d6557@gandalf.local.home> In-Reply-To: References: <8c7de46d-9869-aa5e-2bb9-5dbc2eda395e@linux.alibaba.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?B?546L6LSH?= , "Peter Zijlstra \(Intel\)" , Paul Walmsley , "James E.J. Bottomley" , Guo Ren , Jisheng Zhang , "H. Peter Anvin" , live-patching@vger.kernel.org, linux-riscv@lists.infradead.org, Paul Mackerras , Joe Lawrence , Helge Deller , x86@kernel.org, linux-csky@vger.kernel.org, Ingo Molnar , Petr Mladek , Albert Ou , Jiri Kosina , Nicholas Piggin , Borislav Petkov , Josh Poimboeuf , Thomas Gleixner , linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, Palmer Dabbelt , Masami Hiramatsu , Colin Ian King , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, 12 Oct 2021 14:24:43 +0200 (CEST) Miroslav Benes wrote: > > +++ b/kernel/livepatch/patch.c > > @@ -52,11 +52,6 @@ static void notrace klp_ftrace_handler(unsigned long ip, > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > > if (WARN_ON_ONCE(bit < 0)) > > return; > > - /* > > - * A variant of synchronize_rcu() is used to allow patching functions > > - * where RCU is not watching, see klp_synchronize_transition(). > > - */ > > - preempt_disable_notrace(); > > > > func = list_first_or_null_rcu(&ops->func_stack, struct klp_func, > > stack_node); > > @@ -120,7 +115,6 @@ static void notrace klp_ftrace_handler(unsigned long ip, > > klp_arch_set_pc(fregs, (unsigned long)func->new_func); > > > > unlock: > > - preempt_enable_notrace(); > > ftrace_test_recursion_unlock(bit); > > } > > I don't like this change much. We have preempt_disable there not because > of ftrace_test_recursion, but because of RCU. ftrace_test_recursion was > added later. Yes, it would work with the change, but it would also hide > things which should not be hidden in my opinion. Agreed, but I believe the change is fine, but requires a nice comment to explain what you said above. Thus, before the "ftrace_test_recursion_trylock()" we need: /* * The ftrace_test_recursion_trylock() will disable preemption, * which is required for the variant of synchronize_rcu() that is * used to allow patching functions where RCU is not watching. * See klp_synchronize_transition() for more details. */ -- Steve