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_1 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 933C8C4321A for ; Fri, 28 Jun 2019 01:21:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 62E97214AF for ; Fri, 28 Jun 2019 01:21:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726667AbfF1BVT (ORCPT ); Thu, 27 Jun 2019 21:21:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53530 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726606AbfF1BVT (ORCPT ); Thu, 27 Jun 2019 21:21:19 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 88F9A307D91F; Fri, 28 Jun 2019 01:21:18 +0000 (UTC) Received: from treble (ovpn-126-66.rdu2.redhat.com [10.10.126.66]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 88A9E60BEC; Fri, 28 Jun 2019 01:21:12 +0000 (UTC) Date: Thu, 27 Jun 2019 20:21:09 -0500 From: Josh Poimboeuf To: Steven Rostedt Cc: LKML , 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: Re: [PATCH] ftrace/x86: Add a comment to why we take text_mutex in ftrace_arch_code_modify_prepare() Message-ID: <20190628012109.p7a2whpsnad5vjz7@treble> References: <20190627211819.5a591f52@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190627211819.5a591f52@gandalf.local.home> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Fri, 28 Jun 2019 01:21:18 +0000 (UTC) Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Thu, Jun 27, 2019 at 09:18:19PM -0400, Steven Rostedt wrote: > > 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 > Reviewed-by: Josh Poimboeuf -- Josh