From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754794AbaHAPzv (ORCPT ); Fri, 1 Aug 2014 11:55:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:62008 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751008AbaHAPzu (ORCPT ); Fri, 1 Aug 2014 11:55:50 -0400 Date: Fri, 1 Aug 2014 17:53:10 +0200 From: Oleg Nesterov To: "Paul E. McKenney" 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 v2 tip/core/rcu 01/10] rcu: Add call_rcu_tasks() Message-ID: <20140801155310.GA2945@redhat.com> References: <20140731003914.GA3872@linux.vnet.ibm.com> <1406767182-4356-1-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1406767182-4356-1-git-send-email-paulmck@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 07/30, 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)) { > + t->rcu_tasks_nvcsw = ACCESS_ONCE(t->nvcsw); > + t->rcu_tasks_holdout = 1; > + list_add(&t->rcu_tasks_holdout_list, > + &rcu_tasks_holdouts); > + } > + } > + rcu_read_unlock(); Wait, unless I missed something this can't work... The problem is, once the exiting task passes exit_notify() it can be removed from rcu lists. Now suppose that (say) proc_exit_connector() has a probe, and this task has jumped into trampoline and it was preempted there. No? Oleg.