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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 4F8A2C2D0CE for ; Sat, 25 Jan 2020 02:23:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 25AC22073B for ; Sat, 25 Jan 2020 02:23:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579918986; bh=aXF9h2u0IVG3AMeK/xiBH+gwvZuHauq2rn1H24VHNrk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=Y2Wwk8m8XLYVrfRc9feFXXsLkwzBcFmfXmUHSquhPy8+gx5Gg0xZX82oXCN2J8Wf7 Z0USwszG6qqhmg1WhBnz+hUKFmRSMRR1SSF4jW/xIsSpEBtdDRlEcfeaW1nveqLYEA Hr34Yehz84gv+u9Wd43+1PzRFlKRKPArjrlK8QC8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387721AbgAYCXF (ORCPT ); Fri, 24 Jan 2020 21:23:05 -0500 Received: from mail.kernel.org ([198.145.29.99]:60502 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387542AbgAYCXF (ORCPT ); Fri, 24 Jan 2020 21:23:05 -0500 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (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 302B720718; Sat, 25 Jan 2020 02:23:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579918984; bh=aXF9h2u0IVG3AMeK/xiBH+gwvZuHauq2rn1H24VHNrk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=F0WZwfXQd/GPg5PAw8lYleL2UiAwhc70o7cEyY2SnfkF47KModMcUpRiJBHUvMBXC 5OANQr7FJ2d0XFPc20Xq8bhPkA/xo8uh/3Dr9/IhT7/zD6SbM0/Of3rjOpsklaIzwo SBldtFVuNY80VxeQM9ZIhfV59OqQDrudeihi7vVE= Date: Sat, 25 Jan 2020 11:23:00 +0900 From: Masami Hiramatsu To: Steven Rostedt Cc: LKML , Masami Hiramatsu , Divya Indi Subject: Re: [PATCH] tracing: Decrement trace_array when bootconfig creates an instance Message-Id: <20200125112300.220f1728f6e47f45717ec564@kernel.org> In-Reply-To: <20200124205927.76128804@rorschach.local.home> References: <20200124205927.76128804@rorschach.local.home> X-Mailer: Sylpheed 3.5.1 (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 Fri, 24 Jan 2020 20:59:27 -0500 Steven Rostedt wrote: > > From: "Steven Rostedt (VMware)" > > The trace_array_get_by_name() creates a ftrace instance and > trace_array_put() is used to remove the reference. Even though the > trace_array_get_by_name() creates the instance, it also adds a reference > count to it, that prevents user space from removing it. > > As the bootconfig just creates the instance on boot up, it should still be > used where it can be deleted by user space after boot. A trace_array_put() > is required to let that happen. Otherwise, the created instance can not > be removed. > > Also, change the documentation on trace_array_get_by_name() to make this not > be so confusing. Good catch! I misunderstood trace_array_put() would remove the instance. Acked-by: Masami Hiramatsu Thank you! > > Fixes: 4f712a4d04a4e ("tracing/boot: Add instance node support") > Signed-off-by: Steven Rostedt (VMware) > --- > kernel/trace/trace.c | 4 ++++ > kernel/trace/trace_boot.c | 1 + > 2 files changed, 5 insertions(+) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 6fed9b0a8d58..0a5569b1cace 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -8602,6 +8602,10 @@ static int instance_mkdir(const char *name) > * NOTE: This function increments the reference counter associated with the > * trace array returned. This makes sure it cannot be freed while in use. > * Use trace_array_put() once the trace array is no longer needed. > + * If the trace_array is to be freed, trace_array_destroy() needs to > + * be called after the trace_array_put(), or simply let user space delete > + * it from the tracefs instances directory. But until the > + * trace_array_put() is called, user space can not delete it. > * > */ > struct trace_array *trace_array_get_by_name(const char *name) > diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c > index cd541ac1cbc1..2f616cd926b0 100644 > --- a/kernel/trace/trace_boot.c > +++ b/kernel/trace/trace_boot.c > @@ -327,6 +327,7 @@ trace_boot_init_instances(struct xbc_node *node) > continue; > } > trace_boot_init_one_instance(tr, inode); > + trace_array_put(tr); > } > } > > -- > 2.20.1 > -- Masami Hiramatsu