From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752135AbaHDN2K (ORCPT ); Mon, 4 Aug 2014 09:28:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:16285 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751242AbaHDN2I (ORCPT ); Mon, 4 Aug 2014 09:28:08 -0400 Date: Mon, 4 Aug 2014 15:25:25 +0200 From: Oleg Nesterov To: "Paul E. McKenney" Cc: Lai Jiangshan , linux-kernel@vger.kernel.org, mingo@kernel.org, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, bobby.prani@gmail.com Subject: Re: [PATCH v3 tip/core/rcu 1/9] rcu: Add call_rcu_tasks() Message-ID: <20140804132525.GA18722@redhat.com> References: <20140731215445.GA21933@linux.vnet.ibm.com> <1406843709-23396-1-git-send-email-paulmck@linux.vnet.ibm.com> <20140802145616.GA18195@redhat.com> <20140802225757.GB8101@linux.vnet.ibm.com> <20140803133318.GB671@redhat.com> <20140803220535.GH8101@linux.vnet.ibm.com> <53DED5D1.6030504@cn.fujitsu.com> <20140804010938.GI8101@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140804010938.GI8101@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/03, Paul E. McKenney wrote: > > On Mon, Aug 04, 2014 at 08:37:37AM +0800, Lai Jiangshan wrote: > > An alternative solution: > > srcu_read_lock() before exit_notify(), srcu_read_unlock() after the last preempt_disable() > > in the do_exit, and synchronize_srcu() in rcu_tasks_kthread(). > > That is a good way to synchronize with the exiting tasks, and I will > probably that that approach. > > I -thought- that Oleg was concerned about safely building the list to > start with, though. But for_each_process_thread() under rcu_read_lock() should work except it can miss the exiting tasks. So it seems that the clever Lai's trick should solve the problem. Oleg.