From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752251AbbIFOaB (ORCPT ); Sun, 6 Sep 2015 10:30:01 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:16900 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751828AbbIFO3w (ORCPT ); Sun, 6 Sep 2015 10:29:52 -0400 Message-ID: <55EC4DD7.80208@oracle.com> Date: Sun, 06 Sep 2015 10:29:43 -0400 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Minfei Huang CC: rostedt@goodmis.org, mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ftrace: allow dumping traces without tracking trace started cpus References: <1441385156-27279-1-git-send-email-sasha.levin@oracle.com> <20150906092016.GA20381@dhcp-128-25.nay.redhat.com> In-Reply-To: <20150906092016.GA20381@dhcp-128-25.nay.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/06/2015 05:20 AM, Minfei Huang wrote: > On 09/04/15 at 12:45pm, Sasha Levin wrote: >> > We don't init iter->started when dumping the ftrace buffer, and there's no >> > real need to do so - so allow skipping that check if the iter doesn't have >> > an initialized ->started cpumask. >> > >> > Signed-off-by: Sasha Levin >> > --- >> > kernel/trace/trace.c | 5 +++-- >> > 1 file changed, 3 insertions(+), 2 deletions(-) >> > >> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c >> > index 6e79408..0dc647f 100644 >> > --- a/kernel/trace/trace.c >> > +++ b/kernel/trace/trace.c >> > @@ -2671,13 +2671,14 @@ static void test_cpu_buff_start(struct trace_iterator *iter) >> > if (!(iter->iter_flags & TRACE_FILE_ANNOTATE)) >> > return; >> > >> > - if (cpumask_test_cpu(iter->cpu, iter->started)) >> > + if (iter->started && cpumask_test_cpu(iter->cpu, iter->started)) >> > return; > Ftrace will initialize the variable iter->started in the function > trace_init_global_iter. Otherwise kernel will panic during calling the > function cpumask_test_cpu. > > So it is safe to call the function cpumask_test_cpu without doing > checking. Can you point me to exactly where trace_init_global_iter() initializes iter->started? Thanks, Sasha