From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751754AbdHBAMS (ORCPT ); Tue, 1 Aug 2017 20:12:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:47170 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751677AbdHBAMR (ORCPT ); Tue, 1 Aug 2017 20:12:17 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4D10C22CA0 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Tue, 1 Aug 2017 20:12:14 -0400 From: Steven Rostedt To: Daniel Lezcano Cc: paulmck@linux.vnet.ibm.com, john.stultz@linaro.org, linux-kernel@vger.kernel.org Subject: Re: RCU stall when using function_graph Message-ID: <20170801201214.1e9c7d8e@gandalf.local.home> In-Reply-To: References: <20170801220405.GL3730@linux.vnet.ibm.com> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2 Aug 2017 00:15:44 +0200 Daniel Lezcano wrote: > On 02/08/2017 00:04, Paul E. McKenney wrote: > >> Hi Paul, > >> > >> I have been trying to set the function_graph tracer for ftrace and each time I > >> get a CPU stall. > >> > >> How to reproduce: > >> ----------------- > >> > >> echo function_graph > /sys/kernel/debug/tracing/current_tracer > >> > >> This error appears with v4.13-rc3 and v4.12-rc6. Can you bisect this? It may be due to this commit: 0598e4f08 ("ftrace: Add use of synchronize_rcu_tasks() with dynamic trampolines") -- Steve > >> > >> Is it something already reported ? > > > > I have seen this sort of thing, but only when actually dumping the trace > > out, and I though those got fixed. You are seeing this just accumulating > > the trace? > > No, just by changing the tracer. It is the first operation I do after > rebooting and it is reproducible each time. That happens on an ARM64 > platform. > > > These RCU CPU stall warnings usually occur when something grabs hold of > > a CPU for too long, as in 21 seconds or so. One way that they can happen > > is excessive lock contention, another is having the kernel run through > > too much data at one shot. > > > > Adding Steven Rostedt on CC for his thoughts. > > >