From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756461Ab3HaUmZ (ORCPT ); Sat, 31 Aug 2013 16:42:25 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:7712 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753243Ab3HaUmY (ORCPT ); Sat, 31 Aug 2013 16:42:24 -0400 X-Authority-Analysis: v=2.0 cv=DqnUCRD+ c=1 sm=0 a=Sro2XwOs0tJUSHxCKfOySw==:17 a=Drc5e87SC40A:10 a=9h7nfDi7qgwA:10 a=5SG0PmZfjMsA:10 a=IkcTkHD0fZMA:10 a=meVymXHHAAAA:8 a=KGjhK52YXX0A:10 a=Lovc2pkZwpIA:10 a=suQpZlP5M7fFKTF2m4oA:9 a=QEXdDO2ut3YA:10 a=jeBq3FmKZ4MA:10 a=Sro2XwOs0tJUSHxCKfOySw==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 67.255.60.225 Subject: Re: [RFC][PATCH 12/18 v2] ftrace: Disable RCU unsafe checker when function graph is enabled From: Steven Rostedt To: paulmck@linux.vnet.ibm.com Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Peter Zijlstra , Frederic Weisbecker , Jiri Olsa In-Reply-To: <20130831195550.GR3871@linux.vnet.ibm.com> References: <20130831051117.884125230@goodmis.org> <20130831051702.436132384@goodmis.org> <20130831195550.GR3871@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Sat, 31 Aug 2013 16:42:17 -0400 Message-ID: <1377981737.26624.6.camel@pippen.local.home> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2013-08-31 at 12:55 -0700, Paul E. McKenney wrote: > On Sat, Aug 31, 2013 at 01:11:29AM -0400, Steven Rostedt wrote: > > From: "Steven Rostedt (Red Hat)" > > > > Having the RCU unsafe checker running when function graph is enabled > > can cause a live lock. That's because the RCU unsafe checker enables > > full lockdep debugging on RCU which does a lot of interal calls that > > may be traced by the function graph tacer. This adds quite a bit of > > s/tacer/tracer/ (Yeah, yeah, picky, picky!) > > > overhead and can possibly live lock the system. > > > > Just do not do the RCU unsafe checks when function graph tracer is > > enabled. > > > > Signed-off-by: Steven Rostedt > > One question: How does the user/tester/developer know that RCU-unsafe > checks have been disabled by function-graph tracing? Would it make > sense to print something to dmesg calling this out? Or do the transitions > happen too often? Ideally, (for 3.13) I plan on having this be a sysctl switch. That will be 1 or 0, depending on if it is enabled or not. But yeah, I can add a printk to show that the kernel changed it. It doesn't happen often, and mainly by a user (or selftest). -- Steve > > Thanx, Paul > > > ---