From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765626AbYBTVgo (ORCPT ); Wed, 20 Feb 2008 16:36:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752841AbYBTVgg (ORCPT ); Wed, 20 Feb 2008 16:36:36 -0500 Received: from wx-out-0506.google.com ([66.249.82.230]:11735 "EHLO wx-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751299AbYBTVgf (ORCPT ); Wed, 20 Feb 2008 16:36:35 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:to:cc:content-type:date:message-id:mime-version:x-mailer:content-transfer-encoding; b=Bw8K+/i65hd0hHkp7wZIm2JeB3WSiqrdv+Wdbvr2KCXRLL3W99s81z6k6PmBmSn/zWrMJME1Cod9nBomP5eb7E+CShG6jWmkxRaOK65Mh05CB//0WMMRHJMsdPBcw2VYdPb0cMkljqvz8+gTHsbdCWzlDkHpAvoltC5ohHobssY= Subject: [PATCH 1/2] kthread: add a missing memory barrier to kthread_stop() From: Dmitry Adamushko To: Andrew Morton , linux-kernel@vger.kernel.org Cc: Nick Piggin , Ingo Molnar , Rusty Russel , "Paul E. McKenney" , Peter Zijlstra , Andy Whitcroft , dmitry.adamushko@gmail.com Content-Type: text/plain Date: Wed, 20 Feb 2008 22:36:30 +0100 Message-Id: <1203543390.6307.24.camel@earth> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dmitry Adamushko Subject: kthread: add a missing memory barrier to kthread_stop() We must ensure that kthread_stop_info.k has been updated before kthread's wakeup. This is required to properly support the use of kthread_should_stop() in the main loop of kthread. wake_up_process() doesn't imply a full memory barrier, so we add an explicit one. There is a requirement on how a main loop of kthread has to be orginized. Namely, the sequence of events that lead to kthread being blocked (schedule()) has to be ordered as follows: - set_current_state(TASK_INTERRUPTIBLE); - if (kthread_should_stop()) break; - schedule() or similar. set_current_state() implies a full memory barrier, so this is a matching barrier on the side of kthread_should_stop(). Signed-off-by: Dmitry Adamushko diff --git a/kernel/kthread.c b/kernel/kthread.c index 45f8b83..86b69a0 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -53,6 +53,19 @@ static struct kthread_stop_info kthread_stop_info; * When someone calls kthread_stop() on your kthread, it will be woken * and this will return true. You should then return, and your return * value will be passed through to kthread_stop(). + * + * In order to safely use kthread_stop() for kthread, there is a requirement + * on how its main loop has to be orginized. Namely, the sequence of + * events that lead to kthread being blocked (schedule()) has to be + * ordered as follows: + * + * - set_current_state(TASK_INTERRUPTIBLE); + * - if (kthread_should_stop()) break; + * - schedule() or similar. + * + * set_current_state() implies a full memory barrier. kthread_stop() + * has a matching barrier right after an update of kthread_stop_info.k + * and before kthread's wakeup. */ int kthread_should_stop(void) { @@ -211,6 +224,15 @@ int kthread_stop(struct task_struct *k) /* Now set kthread_should_stop() to true, and wake it up. */ kthread_stop_info.k = k; + + /* + * We must ensure that kthread_stop_info.k has been updated before + * the following wakeup. This is required to properly support the use + * of kthread_should_stop() in the main loop of kthread + * (see description of kthread_should_stop() for more details). + */ + smp_mb(); + wake_up_process(k); put_task_struct(k);