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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53D7CC4332F for ; Tue, 22 Nov 2022 21:32:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235054AbiKVVcf convert rfc822-to-8bit (ORCPT ); Tue, 22 Nov 2022 16:32:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56520 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235040AbiKVVcd (ORCPT ); Tue, 22 Nov 2022 16:32:33 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1FA74B79 for ; Tue, 22 Nov 2022 13:32:30 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id BF583B81DBD for ; Tue, 22 Nov 2022 21:32:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30E12C433C1; Tue, 22 Nov 2022 21:32:27 +0000 (UTC) Date: Tue, 22 Nov 2022 16:32:25 -0500 From: Steven Rostedt To: Song Shuai Cc: mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ftrace: avoid replacing the list func with itself Message-ID: <20221122163225.76a19e1d@gandalf.local.home> In-Reply-To: References: <20221026132039.2236233-1-suagrfillet@gmail.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 22 Nov 2022 02:28:25 +0000 Song Shuai wrote: > Song Shuai 于2022年10月26日周三 13:20写道： > > > > The list func (ftrace_ops_list_func) will be patched first > > before the transition between old and new calls are set, > > which fixed the race described in this commit `59338f75`. > > > > While ftrace_trace_function changes from the list func to a > > ftrace_ops func, like unregistering the klp_ops to leave the only > > global_ops in ftrace_ops_list, the ftrace_[regs]_call will be > > replaced with the list func although it already exists. So there > > should be a condition to avoid this. > > > > This patch backups saved_ftrace_func by saved_ftrace_func_old > > which will be compared with the list func before trying to patch it. > > > Ping... Wouldn't something like this be simpler and easier to manage (without adding another variable to keep track of)? -- Steve diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 65a5d36463e0..d04552c0c275 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -2763,6 +2763,19 @@ void __weak ftrace_arch_code_modify_post_process(void) { } +static int update_ftrace_func(ftrace_func_t func) +{ + static ftrace_func_t save_func; + + /* Avoid updating if it hasn't changed */ + if (func == save_func) + return 0; + + save_func = func; + + return ftrace_update_ftrace_func(func); +} + void ftrace_modify_all_code(int command) { int update = command & FTRACE_UPDATE_TRACE_FUNC; @@ -2783,7 +2796,7 @@ void ftrace_modify_all_code(int command) * traced. */ if (update) { - err = ftrace_update_ftrace_func(ftrace_ops_list_func); + err = update_ftrace_func(ftrace_ops_list_func); if (FTRACE_WARN_ON(err)) return; } @@ -2799,7 +2812,7 @@ void ftrace_modify_all_code(int command) /* If irqs are disabled, we are in stop machine */ if (!irqs_disabled()) smp_call_function(ftrace_sync_ipi, NULL, 1); - err = ftrace_update_ftrace_func(ftrace_trace_function); + err = update_ftrace_func(ftrace_trace_function); if (FTRACE_WARN_ON(err)) return; }