From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935982Ab0COJMW (ORCPT ); Mon, 15 Mar 2010 05:12:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49725 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935894Ab0COJMU (ORCPT ); Mon, 15 Mar 2010 05:12:20 -0400 Date: Mon, 15 Mar 2010 10:10:14 +0100 From: Oleg Nesterov To: Peter Zijlstra , Ingo Molnar Cc: Ben Blum , Jiri Slaby , Lai Jiangshan , Li Zefan , Miao Xie , Paul Menage , "Rafael J. Wysocki" , Tejun Heo , linux-kernel@vger.kernel.org Subject: [PATCH 3/6] move_task_off_dead_cpu: remove retry logic Message-ID: <20100315091014.GA9138@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 The previous patch preserved the retry logic, but it looks unneeded. __migrate_task() can only fail if we raced with migration after we dropped the lock, but in this case the caller of set_cpus_allowed/etc must initiate migration itself if ->on_rq == T. We already fixed p->cpus_allowed, the changes in active/online masks must be visible to racer, it should migrate the task to online cpu correctly. Signed-off-by: Oleg Nesterov --- kernel/sched.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) --- 34-rc1/kernel/sched.c~2_XXX_MTODC_DONT_RETRY 2010-03-15 09:40:31.000000000 +0100 +++ 34-rc1/kernel/sched.c 2010-03-15 09:40:44.000000000 +0100 @@ -5517,7 +5517,7 @@ static void move_task_off_dead_cpu(int d struct rq *rq = cpu_rq(dead_cpu); int needs_cpu, dest_cpu; unsigned long flags; -again: + local_irq_save(flags); raw_spin_lock(&rq->lock); @@ -5525,14 +5525,13 @@ again: if (needs_cpu) dest_cpu = select_fallback_rq(dead_cpu, p); raw_spin_unlock(&rq->lock); - - /* It can have affinity changed while we were choosing. */ + /* + * It can only fail if we race with set_cpus_allowed(), + * in the racer should migrate the task anyway. + */ if (needs_cpu) - needs_cpu = !__migrate_task(p, dead_cpu, dest_cpu); + __migrate_task(p, dead_cpu, dest_cpu); local_irq_restore(flags); - - if (unlikely(needs_cpu)) - goto again; } /*