From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753532AbdDKVuB (ORCPT ); Tue, 11 Apr 2017 17:50:01 -0400 Received: from mail.kernel.org ([198.145.29.136]:44718 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752436AbdDKVt7 (ORCPT ); Tue, 11 Apr 2017 17:49:59 -0400 Date: Tue, 11 Apr 2017 17:49:53 -0400 From: Steven Rostedt To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org Subject: Re: There is a Tasks RCU stall warning Message-ID: <20170411174953.46adbf1e@gandalf.local.home> In-Reply-To: <20170411214443.GH1600@linux.vnet.ibm.com> References: <20170411211802.GA19165@linux.vnet.ibm.com> <20170411173133.52b28cfe@gandalf.local.home> <20170411173447.0bdb9f77@gandalf.local.home> <20170411173900.00f4b6c6@gandalf.local.home> <20170411214443.GH1600@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 Tue, 11 Apr 2017 14:44:43 -0700 "Paul E. McKenney" wrote: > Works for me! > > Hopefully it will also work for your computer. :-) > > And whew! Glad to see that the stall warnings worked! Ah! but I think I found a bug in synchronize_rcu_tasks()! Calling schedule isn't good enough. For rcu_tasks to continue, the task needs to schedule out. With my updated code, I just triggered: [ 196.276868] INFO: rcu_tasks detected stalls on tasks: [ 196.284294] ffff8800c26f8040: .. nvcsw: 2/2 holdout: 1 idle_cpu: -1/1 [ 196.293175] event_benchmark R running task 30536 1127 2 0x10000000 [ 196.302746] Call Trace: [ 196.307640] ? _raw_spin_unlock_irq+0x1f/0x50 [ 196.314453] __schedule+0x222/0x1210 [ 196.320476] ? pci_mmcfg_check_reserved+0xc0/0xc0 [ 196.327616] ? preempt_count_add+0xb7/0xf0 [ 196.334174] ? __asan_store8+0x15/0x70 [ 196.340384] schedule+0x57/0xe0 [ 196.345888] benchmark_event_kthread+0x2e/0x3c0 [ 196.352823] kthread+0x178/0x1d0 [ 196.358411] ? trace_benchmark_reg+0x80/0x80 [ 196.365073] ? kthread_create_on_node+0xa0/0xa0 [ 196.371999] ret_from_fork+0x2e/0x40 And here my benchmark called schedule(), but nothing scheduled it out, and it still fails on rcu_tasks. -- Steve