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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 F0E0FC4360C for ; Thu, 10 Oct 2019 15:03:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D1641206B6 for ; Thu, 10 Oct 2019 15:03:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726395AbfJJPD2 (ORCPT ); Thu, 10 Oct 2019 11:03:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:44486 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725862AbfJJPD2 (ORCPT ); Thu, 10 Oct 2019 11:03:28 -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 9522B206A1; Thu, 10 Oct 2019 15:03:27 +0000 (UTC) Date: Thu, 10 Oct 2019 11:03:26 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: LKML , Jessica Yu , Ingo Molnar Subject: Re: [PATCH] ftrace/module: Allow ftrace to make only loaded module text read-write Message-ID: <20191010110326.75131dbf@gandalf.local.home> In-Reply-To: <20191010105515.5eba7f31@gandalf.local.home> References: <20191009223638.60b78727@oasis.local.home> <20191010073121.GN2311@hirez.programming.kicks-ass.net> <20191010093329.GI2359@hirez.programming.kicks-ass.net> <20191010093650.GJ2359@hirez.programming.kicks-ass.net> <20191010122909.GK2359@hirez.programming.kicks-ass.net> <20191010105515.5eba7f31@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: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 10 Oct 2019 10:55:15 -0400 Steven Rostedt wrote: > But we have an issue with the state of the module here, as it is still > set as MODULE_STATE_UNFORMED. Let's look at what happens if we have: > > > CPU0 CPU1 > ---- ---- > echo function > current_tracer > modprobe foo > enable foo functions to be traced > (foo function records not disabled) > echo nop > current_tracer > > disable all functions being > traced including foo functions > > arch calls set_all_modules_text_rw() > [skips UNFORMED modules, which foo still is ] > > set foo's text to read-only > foo's state to COMING > > tries to disable foo's functions > foo's text is read-only > > BUG trying to write to ro text!!! > > > Like I said, this is very subtle. It may no longer be a bug on x86 > with your patches, but it will bug on ARM or anything else that still > uses set_all_modules_text_rw() in the ftrace prepare code. I guess I should have commented this, but the big reason for the split between ftrace_module_init() and ftrace_module_enable() is that we add the nops when the module is still UNFORMED, but we only enable it when the module is COMING or beyond, and not UNFORMED. -- Steve