From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752684AbaJFVhf (ORCPT ); Mon, 6 Oct 2014 17:37:35 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.227]:38985 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752262AbaJFVgf (ORCPT ); Mon, 6 Oct 2014 17:36:35 -0400 Message-Id: <20141006213631.352752419@goodmis.org> User-Agent: quilt/0.61-1 Date: Mon, 06 Oct 2014 17:35:52 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Linus Torvalds , Ingo Molnar , Andrew Morton , Dave Hansen , Dave Hansen , , Ingo Molnar Subject: [PATCH 08/11] tracing: generate RCU warnings even when tracepoints are disabled References: <20141006213544.344821619@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=0008-tracing-generate-RCU-warnings-even-when-tracepoints-.patch X-RR-Connecting-IP: 107.14.168.142:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen Dave Jones reported seeing a bug from one of my TLB tracepoints: http://lkml.kernel.org/r/20140806181801.GA4605@redhat.com I've been running these patches for months and never saw this. But, a big chunk of my testing, especially with all the debugging enabled, was in a vm where intel_idle doesn't work. On the systems where I was using intel_idle, I never had lockdep enabled and this tracepoint on at the same time. This patch ensures that whenever we have lockdep available, we do _some_ RCU activity at the site of the tracepoint, despite whether the tracepoint's condition matches or even if the tracepoint itself is completely disabled. This is a bit of a hack, but it is pretty self-contained. I confirmed that with this patch plus lockdep I get the same splat as Dave Jones did, but without enabling the tracepoint explicitly. Link: http://lkml.kernel.org/p/20140807175204.C257CAC5@viggo.jf.intel.com Signed-off-by: Dave Hansen Cc: Dave Hansen Cc: Dave Jones , Cc: paulmck@linux.vnet.ibm.com Cc: Ingo Molnar Signed-off-by: Steven Rostedt --- include/linux/tracepoint.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index b1293f15f592..e08e21e5f601 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h @@ -157,6 +157,12 @@ extern void syscall_unregfunc(void); * Make sure the alignment of the structure in the __tracepoints section will * not add unwanted padding between the beginning of the section and the * structure. Force alignment to the same alignment as the section start. + * + * When lockdep is enabled, we make sure to always do the RCU portions of + * the tracepoint code, regardless of whether tracing is on or we match the + * condition. This lets us find RCU issues triggered with tracepoints even + * when this tracepoint is off. This code has no purpose other than poking + * RCU a bit. */ #define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \ extern struct tracepoint __tracepoint_##name; \ @@ -167,6 +173,11 @@ extern void syscall_unregfunc(void); TP_PROTO(data_proto), \ TP_ARGS(data_args), \ TP_CONDITION(cond),,); \ + if (IS_ENABLED(CONFIG_LOCKDEP)) { \ + rcu_read_lock_sched_notrace(); \ + rcu_dereference_sched(__tracepoint_##name.funcs);\ + rcu_read_unlock_sched_notrace(); \ + } \ } \ __DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args), \ PARAMS(cond), PARAMS(data_proto), PARAMS(data_args)) \ -- 2.0.1