From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754768Ab3IYQj4 (ORCPT ); Wed, 25 Sep 2013 12:39:56 -0400 Received: from terminus.zytor.com ([198.137.202.10]:40218 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751283Ab3IYQjw (ORCPT ); Wed, 25 Sep 2013 12:39:52 -0400 Date: Wed, 25 Sep 2013 09:39:20 -0700 From: tip-bot for Peter Zijlstra Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched: Prepare for per-cpu preempt_count Git-Commit-ID: a233f1120c37724938f7201fe2353b2577adaaf9 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (terminus.zytor.com [127.0.0.1]); Wed, 25 Sep 2013 09:39:26 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: a233f1120c37724938f7201fe2353b2577adaaf9 Gitweb: http://git.kernel.org/tip/a233f1120c37724938f7201fe2353b2577adaaf9 Author: Peter Zijlstra AuthorDate: Mon, 23 Sep 2013 19:04:26 +0200 Committer: Ingo Molnar CommitDate: Wed, 25 Sep 2013 14:07:55 +0200 sched: Prepare for per-cpu preempt_count When using per-cpu preempt_count variables we need to save/restore the preempt_count on context switch (into per task storage; for instance the old thread_info::preempt_count variable) because of PREEMPT_ACTIVE. However, this means that on fork() the preempt_count value of the last context switch gets copied and if we had a PREEMPT_ACTIVE switch right before cloning a child task the child task will now too have PREEMPT_ACTIVE set and start its life with an extra PREEMPT_ACTIVE count. Therefore we need to make init_task_preempt_count() unconditional; this resets whatever preempt_count we inherited from our parent process. Doing so for !per-cpu implementations is harmless. For !PREEMPT_COUNT kernels we need to be careful not to start life with an increased preempt_count. Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-4k0b7oy1rcdyzochwiixuwi9@git.kernel.org Signed-off-by: Ingo Molnar --- include/linux/sched.h | 12 +++++++++--- kernel/sched/core.c | 2 -- 2 files changed, 9 insertions(+), 5 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 06ac17c..b09798b 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -428,6 +428,14 @@ struct task_cputime { .sum_exec_runtime = 0, \ } +#define PREEMPT_ENABLED (PREEMPT_NEED_RESCHED) + +#ifdef CONFIG_PREEMPT_COUNT +#define PREEMPT_DISABLED (1 + PREEMPT_ENABLED) +#else +#define PREEMPT_DISABLED PREEMPT_ENABLED +#endif + /* * Disable preemption until the scheduler is running. * Reset by start_kernel()->sched_init()->init_idle(). @@ -435,9 +443,7 @@ struct task_cputime { * We include PREEMPT_ACTIVE to avoid cond_resched() from working * before the scheduler is active -- see should_resched(). */ -#define INIT_PREEMPT_COUNT (1 + PREEMPT_ACTIVE + PREEMPT_NEED_RESCHED) -#define PREEMPT_ENABLED (PREEMPT_NEED_RESCHED) -#define PREEMPT_DISABLED (1 + PREEMPT_NEED_RESCHED) +#define INIT_PREEMPT_COUNT (PREEMPT_DISABLED + PREEMPT_ACTIVE) /** * struct thread_group_cputimer - thread group interval timer counts diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 9c84a9a..f575d5b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1722,9 +1722,7 @@ void sched_fork(struct task_struct *p) #if defined(CONFIG_SMP) p->on_cpu = 0; #endif -#ifdef CONFIG_PREEMPT_COUNT init_task_preempt_count(p); -#endif #ifdef CONFIG_SMP plist_node_init(&p->pushable_tasks, MAX_PRIO); #endif