From patchwork Tue Nov 22 23:09:05 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 13052844 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 1781CC4332F for ; Tue, 22 Nov 2022 23:09:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235190AbiKVXJR (ORCPT ); Tue, 22 Nov 2022 18:09:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35096 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235214AbiKVXJP (ORCPT ); Tue, 22 Nov 2022 18:09:15 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B6391C495A; Tue, 22 Nov 2022 15:09:10 -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 461D0B81D4B; Tue, 22 Nov 2022 23:09:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 923E5C433D6; Tue, 22 Nov 2022 23:09:07 +0000 (UTC) Date: Tue, 22 Nov 2022 18:09:05 -0500 From: Steven Rostedt To: LKML , Linux Trace Kernel Cc: Masami Hiramatsu , Song Shuai Subject: [PATCH] ftrace: Avoid needless updates of the ftrace function call Message-ID: <20221122180905.737b6f52@gandalf.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org From: "Steven Rostedt (Google)" Song Shuai reported: 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. And suggested using another variable to keep track of what the ftrace function is set to. But this could be simplified by using a helper function that does the same with a static variable. Link: https://lore.kernel.org/lkml/20221026132039.2236233-1-suagrfillet@gmail.com/ Reported-by: Song Shuai Signed-off-by: Steven Rostedt (Google) Reviewed-by: Masami Hiramatsu (Google) --- kernel/trace/ftrace.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) 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; }