From patchwork Thu Jul 13 15:46:26 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 13312441 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 9E7B2C0015E for ; Thu, 13 Jul 2023 15:46:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231415AbjGMPqb (ORCPT ); Thu, 13 Jul 2023 11:46:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48014 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229691AbjGMPqa (ORCPT ); Thu, 13 Jul 2023 11:46:30 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 45AD52686; Thu, 13 Jul 2023 08:46:29 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D59F661881; Thu, 13 Jul 2023 15:46:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BB775C433C7; Thu, 13 Jul 2023 15:46:27 +0000 (UTC) Date: Thu, 13 Jul 2023 11:46:26 -0400 From: Steven Rostedt To: LKML , Linux Trace Kernel Cc: Masami Hiramatsu , Mark Rutland , Zheng Yejian Subject: [PATCH 1/2] tracing: Remove unnecessary copying of tr->current_trace Message-ID: <20230713114626.704ebe8e@gandalf.local.home> In-Reply-To: <20230713114510.04c452ca@gandalf.local.home> References: <20230713114510.04c452ca@gandalf.local.home> X-Mailer: Claws Mail 3.19.1 (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)" I have no idea why the iterator had to allocate a descriptor to make a copy of "current_trace" (now "tr->current_trace"). The content of that pointer never changes, so it's sufficient to just copy the pointer to maintain integrity with reading it. This is more of a clean up than a fix. Fixes: d7350c3f45694 ("tracing/core: make the read callbacks reentrants") Signed-off-by: Steven Rostedt (Google) Reviewed-by: Masami Hiramatsu (Google) --- kernel/trace/trace.c | 22 +++------------------- 1 file changed, 3 insertions(+), 19 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index be847d45d81c..1c370ffbe062 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4205,15 +4205,9 @@ static void *s_start(struct seq_file *m, loff_t *pos) loff_t l = 0; int cpu; - /* - * copy the tracer to avoid using a global lock all around. - * iter->trace is a copy of current_trace, the pointer to the - * name may be used instead of a strcmp(), as iter->trace->name - * will point to the same string as current_trace->name. - */ mutex_lock(&trace_types_lock); - if (unlikely(tr->current_trace && iter->trace->name != tr->current_trace->name)) - *iter->trace = *tr->current_trace; + if (unlikely(tr->current_trace != iter->trace)) + iter->trace = tr->current_trace; mutex_unlock(&trace_types_lock); #ifdef CONFIG_TRACER_MAX_TRACE @@ -4862,16 +4856,8 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot) iter->fmt = NULL; iter->fmt_size = 0; - /* - * We make a copy of the current tracer to avoid concurrent - * changes on it while we are reading. - */ mutex_lock(&trace_types_lock); - iter->trace = kzalloc(sizeof(*iter->trace), GFP_KERNEL); - if (!iter->trace) - goto fail; - - *iter->trace = *tr->current_trace; + iter->trace = tr->current_trace; if (!zalloc_cpumask_var(&iter->started, GFP_KERNEL)) goto fail; @@ -4936,7 +4922,6 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot) fail: mutex_unlock(&trace_types_lock); - kfree(iter->trace); kfree(iter->temp); kfree(iter->buffer_iter); release: @@ -5021,7 +5006,6 @@ static int tracing_release(struct inode *inode, struct file *file) free_cpumask_var(iter->started); kfree(iter->fmt); kfree(iter->temp); - kfree(iter->trace); kfree(iter->buffer_iter); seq_release_private(inode, file);