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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 F2D24C4360C for ; Thu, 10 Oct 2019 17:01:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C42C62067B for ; Thu, 10 Oct 2019 17:01:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ghFet/M2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726562AbfJJRBR (ORCPT ); Thu, 10 Oct 2019 13:01:17 -0400 Received: from merlin.infradead.org ([205.233.59.134]:33390 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726038AbfJJRBR (ORCPT ); Thu, 10 Oct 2019 13:01:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=aaCNf5DPTtnvU+MCaAQMV2HAXaDI7hDnwEEid6nSG7Q=; b=ghFet/M20GTnBUrx3E0tuNKN+ NlMX7n5wHzf2qCV7jUJ+RoPVbkslDs9JwV0xRuV9pwPwS7w2tLt48ohxDhUbpw7Npvel2KpG9ugG/ 3jHHtlOhhz3BEFuxBAIcZsHyrl1u/mXeulVRqK+OkAWSVi5OYjlqVB5A2q54yKIq4UL0uAePOiDiC pGS/1ctYOqo80G2ae+cw9Phc8poev9/QOTx3tTH9lPOQhq5SmE8emBjJVRRdXkh1Wj7to62R32QPi WV0gaMzbU5UTKEv2lfdi012aBo60XN+gVwU6hlLvL33H6gwYzmnB4f0YzKoQuovntjER8JZzWHX6U dJchBBQLA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iIboQ-000298-ME; Thu, 10 Oct 2019 17:01:14 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id ABAFF3008C1; Thu, 10 Oct 2019 19:00:19 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 03B2C220F94C3; Thu, 10 Oct 2019 19:01:11 +0200 (CEST) Date: Thu, 10 Oct 2019 19:01:11 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: LKML , Jessica Yu , Ingo Molnar Subject: Re: [PATCH] ftrace/module: Allow ftrace to make only loaded module text read-write Message-ID: <20191010170111.GQ2328@hirez.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191010105515.5eba7f31@gandalf.local.home> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 10, 2019 at 10:55:15AM -0400, Steven Rostedt wrote: > OK, so basically this moves the enabling of function tracing from > within the ftrace_module_enable() code without releasing the > ftrace_lock mutex. > > 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 can't immediately follow, but I think we really should go there. For now, something like this might work: --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -34,6 +34,8 @@ #ifdef CONFIG_DYNAMIC_FTRACE +static int ftrace_poke_late = 0; + int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex) { @@ -43,12 +45,15 @@ int ftrace_arch_code_modify_prepare(void * ftrace has it set to "read/write". */ mutex_lock(&text_mutex); + ftrace_poke_late = 1; return 0; } int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex) { + text_poke_finish(); + ftrace_poke_late = 0; mutex_unlock(&text_mutex); return 0; } @@ -116,7 +121,10 @@ ftrace_modify_code_direct(unsigned long return ret; /* replace the text with the new text */ - text_poke_early((void *)ip, new_code, MCOUNT_INSN_SIZE); + if (ftrace_poke_late) + text_poke_queue((void *)ip, new_code, MCOUNT_INSN_SIZE, NULL); + else + text_poke_early((void *)ip, new_code, MCOUNT_INSN_SIZE); return 0; }