From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751916AbdHCOiI (ORCPT ); Thu, 3 Aug 2017 10:38:08 -0400 Received: from mail-wr0-f182.google.com ([209.85.128.182]:38558 "EHLO mail-wr0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751158AbdHCOiF (ORCPT ); Thu, 3 Aug 2017 10:38:05 -0400 Date: Thu, 3 Aug 2017 16:38:01 +0200 From: Daniel Lezcano To: "Paul E. McKenney" Cc: Steven Rostedt , john.stultz@linaro.org, linux-kernel@vger.kernel.org, Pratyush Anand Subject: Re: RCU stall when using function_graph Message-ID: <20170803143801.GE1919@mai> References: <20170801220405.GL3730@linux.vnet.ibm.com> <20170801201214.1e9c7d8e@gandalf.local.home> <20170802124239.GD1919@mai> <20170802090744.6922e9e9@gandalf.local.home> <11d179df-d8a9-5d3e-3bc4-080df464e85d@linaro.org> <20170803124421.GP3730@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170803124421.GP3730@linux.vnet.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 03, 2017 at 05:44:21AM -0700, Paul E. McKenney wrote: [ ... ] > > > BTW, function_graph tracer is the most invasive of the tracers. It's 4x > > > slower than function tracer. I'm wondering if the tracer isn't the > > > cause, but just slows things down enough to cause a some other race > > > condition that triggers the bug. > > > > Yes, that could be true. > > > > I tried the following scenario: > > > > - cpufreq governor => userspace + max_freq (1.2GHz) > > - function_graph set ==> OK > > > > - cpufreq governor => userspace + min_freq (200MHz) > > - function_graph set ==> RCU stall > > > > Beside that, I realize the board is constantly processing SOF interrupts > > every 124us, so that adds more overhead. > > > > Removing the USB support, thus the associated processing for the SOF > > interrupts, I don't see anymore the RCU stall. > > Looks like Steve called this one! ;-) Yep :) > > Is it the expected behavior to have the system hang after a RCU stall > > raises ? > > No, but if NMI stack traces are enabled and there are any NMI problems, > bad things can happen. In addition, the bulk of output can cause problems > if you have a slow console connection. Ok, thanks. -- Daniel -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog