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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 94063ECDE5F for ; Tue, 24 Jul 2018 02:25:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4C67F20874 for ; Tue, 24 Jul 2018 02:25:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4C67F20874 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388352AbeGXD3o (ORCPT ); Mon, 23 Jul 2018 23:29:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:56640 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388194AbeGXD3o (ORCPT ); Mon, 23 Jul 2018 23:29:44 -0400 Received: from vmware.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (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 AA6A420874; Tue, 24 Jul 2018 02:25:36 +0000 (UTC) Date: Mon, 23 Jul 2018 22:25:34 -0400 From: Steven Rostedt To: Masami Hiramatsu Cc: Ingo Molnar , Shuah Khan , Tom Zanussi , Hiraku Toyooka , linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 2/3] [BUGFIX] ring_buffer: tracing: Inherit the tracing setting to next ring buffer Message-ID: <20180723222534.368ea01b@vmware.local.home> In-Reply-To: <153149929558.11274.11730609978254724394.stgit@devbox> References: <153149923649.11274.14970833360963898112.stgit@devbox> <153149929558.11274.11730609978254724394.stgit@devbox> X-Mailer: Claws Mail 3.15.1 (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 Sat, 14 Jul 2018 01:28:15 +0900 Masami Hiramatsu wrote: > Inherit the tracing on/off setting on ring_buffer to next > trace buffer when taking a snapshot. > > Taking a snapshot is done by swapping with backup ring buffer > (max_tr_buffer). But since the tracing on/off setting is set > in the ring buffer, when swapping it, tracing on/off setting > can also be changed. This causes a strange result like below; > > /sys/kernel/debug/tracing # cat tracing_on > 1 > /sys/kernel/debug/tracing # echo 0 > tracing_on > /sys/kernel/debug/tracing # echo 1 > snapshot > /sys/kernel/debug/tracing # cat tracing_on > 1 > /sys/kernel/debug/tracing # echo 1 > snapshot > /sys/kernel/debug/tracing # cat tracing_on > 0 > > We don't touch tracing_on, but snapshot changes tracing_on > setting each time. This must be a bug, because user never know > that each "ring_buffer" stores tracing-enable state and > snapshot is done by swapping ring buffers. > > This patch fixes above strange behavior. > OK, so the issue is that the tracing_on state is saved with the buffer itself. And when we swap the buffer, we also swap the state. > Fixes: commit debdd57f5145 ("tracing: Make a snapshot feature available from userspace") > Signed-off-by: Masami Hiramatsu > Cc: Steven Rostedt > Cc: Ingo Molnar > Cc: Hiraku Toyooka > Cc: stable@vger.kernel.org > --- > include/linux/ring_buffer.h | 1 + > kernel/trace/ring_buffer.c | 12 ++++++++++++ > kernel/trace/trace.c | 6 ++++++ > 3 files changed, 19 insertions(+) > > diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h > index b72ebdff0b77..003d09ab308d 100644 > --- a/include/linux/ring_buffer.h > +++ b/include/linux/ring_buffer.h > @@ -165,6 +165,7 @@ void ring_buffer_record_enable(struct ring_buffer *buffer); > void ring_buffer_record_off(struct ring_buffer *buffer); > void ring_buffer_record_on(struct ring_buffer *buffer); > int ring_buffer_record_is_on(struct ring_buffer *buffer); > +int ring_buffer_record_is_set_on(struct ring_buffer *buffer); > void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu); > void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu); > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 6a46af21765c..4038ed74ab95 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -3227,6 +3227,18 @@ int ring_buffer_record_is_on(struct ring_buffer *buffer) > } > > /** > + * ring_buffer_record_is_set_on - return true if the ring buffer is set writable > + * @buffer: The ring buffer to see if write is set enabled > + * > + * Returns true if the ring buffer is set writable by ring_buffer_record_on(). > + * Note that this does NOT mean it is in a writable state. I'd add a little more context here. Something like: * It may return true when the ring buffer has been disabled by * ring_buffer_record_disable(), as that is a temporary disabling of * the ring buffer. -- Steve > + */ > +int ring_buffer_record_is_set_on(struct ring_buffer *buffer) > +{ > + return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF); > +} > + > +/** > * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer > * @buffer: The ring buffer to stop writes to. > * @cpu: The CPU buffer to stop > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 2556d8c097d2..bbd5a94a7ef1 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -1378,6 +1378,12 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu) > > arch_spin_lock(&tr->max_lock); > > + /* Inherit the recordable setting from trace_buffer */ > + if (ring_buffer_record_is_set_on(tr->trace_buffer.buffer)) > + ring_buffer_record_on(tr->max_buffer.buffer); > + else > + ring_buffer_record_off(tr->max_buffer.buffer); > + > swap(tr->trace_buffer.buffer, tr->max_buffer.buffer); > > __update_max_tr(tr, tsk, cpu);