From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752540AbaHCWFn (ORCPT ); Sun, 3 Aug 2014 18:05:43 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:46999 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751769AbaHCWFm (ORCPT ); Sun, 3 Aug 2014 18:05:42 -0400 Date: Sun, 3 Aug 2014 15:05:35 -0700 From: "Paul E. McKenney" To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, 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: <20140803220535.GH8101@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140803133318.GB671@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14080322-7164-0000-0000-00000390332F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 03, 2014 at 03:33:18PM +0200, Oleg Nesterov wrote: > On 08/02, Paul E. McKenney wrote: > > > > On Sat, Aug 02, 2014 at 04:56:16PM +0200, Oleg Nesterov wrote: > > > On 07/31, Paul E. McKenney wrote: > > > > > > > > + rcu_read_lock(); > > > > + for_each_process_thread(g, t) { > > > > + if (t != current && ACCESS_ONCE(t->on_rq) && > > > > + !is_idle_task(t)) { > > > > > > I didn't notice this check before, but it is not needed. for_each_process() > > > can see the idle threads, there are not on process/thread lists. > ^^^^^^^ > > argh, I mean't "can't see" of course... > > > Good to know. Any other important tasks I am missing? > > Nothing else. Whew! ;-) > > I am guessing that I need to do something like this: > > > > for_each_process(g) { > > /* Do build step. */ > > for_each_thread(g, t) { > > if (g == t) > > continue; > > /* Do build step. */ > > } > > } > > Sorry, I don't understand... This is equivalent to > > for_each_process_thread(g, t) { > /* Do build step. */ > } OK, got it. > > Your point about exiting tasks I get, and I believe I can solve it. > > I am hoping that the above sort of construction takes care of the > > idle threads. > > It is simple to find the idle threads, just > > for_each_cpu(cpu) { > do_something(cpu_rq(cpu)->idle); > } > > but it is not clear to me what else you need to do with the idle threads. > Probably not too much, they mostly run under preempt_disable(). OK, looks easy enough. And yes, one good question is what, if anything, we need to do with the idle threads. > > I might also need to do something to handle changes in > > process/thread hierarchy -- but hopefully without having to read-acquire > > the task-list lock. > > It seems that you need another global list, a task should be visible on that > list until exit_rcu(). As in create another global list that all tasks are added to when created and then remved from when they exit? Thanx, Paul