From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754715AbaHGR4g (ORCPT ); Thu, 7 Aug 2014 13:56:36 -0400 Received: from mga01.intel.com ([192.55.52.88]:30410 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750760AbaHGR4f (ORCPT ); Thu, 7 Aug 2014 13:56:35 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.01,819,1400050800"; d="scan'208";a="573264775" Subject: [PATCH] tracing: generate RCU warnings even when tracepoints are disabled To: linux-kernel@vger.kernel.org Cc: Dave Hansen , dave.hansen@linux.intel.com, davej@redhat.com, paulmck@linux.vnet.ibm.com, rostedt@goodmis.org, mingo@redhat.com From: Dave Hansen Date: Thu, 07 Aug 2014 10:52:04 -0700 Message-Id: <20140807175204.C257CAC5@viggo.jf.intel.com> 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. Signed-off-by: Dave Hansen Cc: Dave Jones , Cc: paulmck@linux.vnet.ibm.com Cc: Steven Rostedt Cc: Ingo Molnar --- b/include/linux/tracepoint.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff -puN include/linux/tracepoint.h~easier-rcu-splat include/linux/tracepoint.h --- a/include/linux/tracepoint.h~easier-rcu-splat 2014-08-07 10:29:32.701217956 -0700 +++ b/include/linux/tracepoint.h 2014-08-07 10:40:35.244627014 -0700 @@ -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)) \ _