From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751532Ab1LZRRj (ORCPT ); Mon, 26 Dec 2011 12:17:39 -0500 Received: from mx1.redhat.com ([209.132.183.28]:28432 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751124Ab1LZRRh (ORCPT ); Mon, 26 Dec 2011 12:17:37 -0500 Date: Mon, 26 Dec 2011 18:11:51 +0100 From: Oleg Nesterov To: Yasunori Goto Cc: Peter Zijlstra , Ingo Molnar , Hiroyuki KAMEZAWA , Motohiro Kosaki , Linux Kernel ML Subject: Re: [BUG] TASK_DEAD task is able to be woken up in special condition Message-ID: <20111226171151.GA4472@redhat.com> References: <1324633794.24803.48.camel@twins> <20111223154137.GA27901@redhat.com> <20111226172357.CE4D.E1E9C6FF@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111226172357.CE4D.E1E9C6FF@jp.fujitsu.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 12/26, Yasunori Goto wrote: > > > > > IIRC, this was already discussed a bit. Say, try_to_wake_up(TASK_INTERRUPTIBLE) > > can wakeup a TASK_UNINTERRUPTIBLE task if it temporary sets INTERRUPTIBLE but > > doesn't call schedule() in this state. > > Oleg-san, > > Could you point the discussion? > I don't understand yet how it occurred... Suppose that the task T does set_current_state(TASK_INTERRUPTIBLE); set_current_state(TASK_UNINTERRUPTIBLE); schedule(); try_to_wake_up(TASK_UNINTERRUPTIBLE) in between can observe this task in TASK_INTERRUPTIBLE state. Then it can set RUNNING/WAKING after T sets ->state = TASK_UNINTERRUPTIBLE. For example, this is possibly if T simply does wait_event() twice when the the 1st wait_event() doesn't sleep. Basically this is the same race you described, but I think you found the case when we can't tolerate the spurious wakeup. Oleg.