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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 57F3EC5B576 for ; Thu, 27 Jun 2019 23:09:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 39FFE2086D for ; Thu, 27 Jun 2019 23:09:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726667AbfF0XJu (ORCPT ); Thu, 27 Jun 2019 19:09:50 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:60043 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726506AbfF0XJu (ORCPT ); Thu, 27 Jun 2019 19:09:50 -0400 Received: from p5b06daab.dip0.t-ipconnect.de ([91.6.218.171] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hgdVt-0002QR-4D; Fri, 28 Jun 2019 01:09:09 +0200 Date: Fri, 28 Jun 2019 01:09:08 +0200 (CEST) From: Thomas Gleixner To: Steven Rostedt cc: Josh Poimboeuf , Petr Mladek , Miroslav Benes , Jessica Yu , Jiri Kosina , Joe Lawrence , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, Johannes Erdfelt , Ingo Molnar , mhiramat@kernel.org, torvalds@linux-foundation.org Subject: Re: [PATCH] ftrace: Remove possible deadlock between register_kprobe() and ftrace_run_update_code() In-Reply-To: <20190627190457.703a486e@gandalf.local.home> Message-ID: References: <20190627081334.12793-1-pmladek@suse.com> <20190627224729.tshtq4bhzhneq24w@treble> <20190627190457.703a486e@gandalf.local.home> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 27 Jun 2019, Steven Rostedt wrote: > On Thu, 27 Jun 2019 17:47:29 -0500 > > Releasing the lock in a separate function seems a bit surprising and > > fragile, would it be possible to do something like this instead? > > > > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c > > index b38c388d1087..89ea1af6fd13 100644 > > --- a/arch/x86/kernel/ftrace.c > > +++ b/arch/x86/kernel/ftrace.c > > @@ -37,15 +37,21 @@ > > int ftrace_arch_code_modify_prepare(void) > > { > > mutex_lock(&text_mutex); > > + > > set_kernel_text_rw(); > > set_all_modules_text_rw(); > > + > > + mutex_unlock(&text_mutex); > > return 0; > > } > > > > int ftrace_arch_code_modify_post_process(void) > > { > > + mutex_lock(&text_mutex); > > + > > set_all_modules_text_ro(); > > set_kernel_text_ro(); > > + > > mutex_unlock(&text_mutex); > > return 0; > > } > > I agree with Josh on this. As the original bug was the race between > ftrace and live patching / modules changing the text from ro to rw and > vice versa. Just protecting the update to the text permissions is more > robust, and should be more self documenting when we need to handle > other architectures for this. How is that supposed to work? ftrace prepare() setrw() setro() patch <- FAIL Thanks, tglx