From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751352Ab3CKRim (ORCPT ); Mon, 11 Mar 2013 13:38:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52458 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752462Ab3CKRik (ORCPT ); Mon, 11 Mar 2013 13:38:40 -0400 Date: Mon, 11 Mar 2013 18:36:43 +0100 From: Oleg Nesterov To: Andrew Morton , Thomas Gleixner Cc: Namhyung Kim , "Paul E. McKenney" , Peter Zijlstra , Rusty Russell , "Srivatsa S. Bhat" , linux-kernel@vger.kernel.org Subject: [PATCH 1/2] kthread: introduce to_live_kthread() Message-ID: <20130311173643.GA13543@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130311173625.GA13525@redhat.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 "k->vfork_done != NULL" with a barrier() after to_kthread(k) in task_get_live_kthread(k) looks unclear, and sub-optimal because we load ->vfork_done twice. All we need is to ensure that we do not return to_kthread(NULL). Add a new trivial helper which loads/checks ->vfork_done once, this also looks more understandable. Signed-off-by: Oleg Nesterov --- kernel/kthread.c | 26 ++++++++++++++++---------- 1 files changed, 16 insertions(+), 10 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index 691dc2e..fa4a013 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -52,8 +52,21 @@ enum KTHREAD_BITS { KTHREAD_IS_PARKED, }; -#define to_kthread(tsk) \ - container_of((tsk)->vfork_done, struct kthread, exited) +#define __to_kthread(vfork) \ + container_of(vfork, struct kthread, exited) + +static inline struct kthread *to_kthread(struct task_struct *k) +{ + return __to_kthread(k->vfork_done); +} + +static struct kthread *to_live_kthread(struct task_struct *k) +{ + struct completion *vfork = ACCESS_ONCE(k->vfork_done); + if (likely(vfork)) + return __to_kthread(vfork); + return NULL; +} /** * kthread_should_stop - should this kthread return now? @@ -313,15 +326,8 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data), static struct kthread *task_get_live_kthread(struct task_struct *k) { - struct kthread *kthread; - get_task_struct(k); - kthread = to_kthread(k); - /* It might have exited */ - barrier(); - if (k->vfork_done != NULL) - return kthread; - return NULL; + return to_live_kthread(k); } /** -- 1.5.5.1