From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754855AbaHGSOA (ORCPT ); Thu, 7 Aug 2014 14:14:00 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:51584 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750890AbaHGSN7 (ORCPT ); Thu, 7 Aug 2014 14:13:59 -0400 Date: Thu, 7 Aug 2014 11:13:56 -0700 From: "Paul E. McKenney" To: Dave Hansen Cc: linux-kernel@vger.kernel.org, dave.hansen@linux.intel.com, davej@redhat.com, rostedt@goodmis.org, mingo@redhat.com Subject: Re: [PATCH] tracing: generate RCU warnings even when tracepoints are disabled Message-ID: <20140807181356.GG5821@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140807175204.C257CAC5@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140807175204.C257CAC5@viggo.jf.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14080718-0928-0000-0000-000003F4BBEB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 07, 2014 at 10:52:04AM -0700, Dave Hansen wrote: > > 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 Looks good to me, but I must defer to Steven on this one. Thanx, Paul > --- > > 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)) \ > _ >