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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=unavailable 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 D381EC4321A for ; Fri, 28 Jun 2019 01:18:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B054F2147A for ; Fri, 28 Jun 2019 01:18:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726633AbfF1BSX (ORCPT ); Thu, 27 Jun 2019 21:18:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:51456 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726606AbfF1BSX (ORCPT ); Thu, 27 Jun 2019 21:18:23 -0400 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 048B0208CB; Fri, 28 Jun 2019 01:18:20 +0000 (UTC) Date: Thu, 27 Jun 2019 21:18:19 -0400 From: Steven Rostedt To: LKML Cc: Josh Poimboeuf , Thomas Gleixner , Petr Mladek , Miroslav Benes , Jessica Yu , Jiri Kosina , Joe Lawrence , live-patching@vger.kernel.org, Johannes Erdfelt , Ingo Molnar , mhiramat@kernel.org, torvalds@linux-foundation.org Subject: [PATCH] ftrace/x86: Add a comment to why we take text_mutex in ftrace_arch_code_modify_prepare() Message-ID: <20190627211819.5a591f52@gandalf.local.home> X-Mailer: Claws Mail 3.17.3 (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: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org From: "Steven Rostedt (VMware)" Taking the text_mutex in ftrace_arch_code_modify_prepare() is to fix a race against module loading and live kernel patching that might try to change the text permissions while ftrace has it as read/write. This really needs to be documented in the code. Add a comment that does such. Suggested-by: Josh Poimboeuf Signed-off-by: Steven Rostedt (VMware) --- arch/x86/kernel/ftrace.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 33786044d5ac..d7e93b2783fd 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -36,6 +36,11 @@ int ftrace_arch_code_modify_prepare(void) { + /* + * Need to grab text_mutex to prevent a race from module loading + * and live kernel patching from changing the text permissions while + * ftrace has it set to "read/write". + */ mutex_lock(&text_mutex); set_kernel_text_rw(); set_all_modules_text_rw(); -- 2.20.1