From patchwork Wed Dec 5 18:44:03 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Srivatsa S. Bhat" X-Patchwork-Id: 1842751 Return-Path: X-Original-To: patchwork-linux-pm@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork2.kernel.org (Postfix) with ESMTP id 2A7AADF266 for ; Wed, 5 Dec 2012 18:47:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753544Ab2LESpi (ORCPT ); Wed, 5 Dec 2012 13:45:38 -0500 Received: from e28smtp02.in.ibm.com ([122.248.162.2]:41907 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753893Ab2LESpd (ORCPT ); Wed, 5 Dec 2012 13:45:33 -0500 Received: from /spool/local by e28smtp02.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Bhat" Subject: [RFC PATCH v2 06/10] sched, cpu hotplug: Use stable online cpus in try_to_wake_up() & select_task_rq() To: tglx@linutronix.de, peterz@infradead.org, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, vincent.guittot@linaro.org, tj@kernel.org, oleg@redhat.com Cc: sbw@mit.edu, amit.kucheria@linaro.org, rostedt@goodmis.org, rjw@sisk.pl, srivatsa.bhat@linux.vnet.ibm.com, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 06 Dec 2012 00:14:03 +0530 Message-ID: <20121205184401.3750.67576.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20121205184041.3750.64945.stgit@srivatsabhat.in.ibm.com> References: <20121205184041.3750.64945.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12120518-5816-0000-0000-000005B2BD6A Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Once stop_machine() is gone from the CPU offline path, we won't be able to depend on preempt_disable() to prevent CPUs from going offline from under us. Use the get/put_online_cpus_atomic_light() APIs to prevent changes to the cpu_online_mask, while invoking from atomic context. Scheduler functions such as try_to_wake_up() and select_task_rq() (and even select_fallback_rq()) deal with picking new CPUs to run tasks. They care only about the cpu_online_mask and not really about the actual CPU tear-down. So they qualify as "light" atomic readers. So use the _light() variant of the APIs. Signed-off-by: Srivatsa S. Bhat --- kernel/sched/core.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 2d8927f..c9a331e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1103,6 +1103,10 @@ EXPORT_SYMBOL_GPL(kick_process); #ifdef CONFIG_SMP /* * ->cpus_allowed is protected by both rq->lock and p->pi_lock + * + * Must be called under get/put_online_cpus_atomic_light() or + * equivalent, to avoid CPUs from going offline from underneath + * us. */ static int select_fallback_rq(int cpu, struct task_struct *p) { @@ -1166,6 +1170,9 @@ out: /* * The caller (fork, wakeup) owns p->pi_lock, ->cpus_allowed is stable. + * + * Must be called under get/put_online_cpus_atomic_light(), to prevent + * CPUs from going offline from underneath us. */ static inline int select_task_rq(struct task_struct *p, int sd_flags, int wake_flags) @@ -1406,6 +1413,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) int cpu, success = 0; smp_wmb(); + get_online_cpus_atomic_light(); raw_spin_lock_irqsave(&p->pi_lock, flags); if (!(p->state & state)) goto out; @@ -1446,6 +1454,7 @@ stat: ttwu_stat(p, cpu, wake_flags); out: raw_spin_unlock_irqrestore(&p->pi_lock, flags); + put_online_cpus_atomic_light(); return success; } @@ -1624,6 +1633,7 @@ void wake_up_new_task(struct task_struct *p) unsigned long flags; struct rq *rq; + get_online_cpus_atomic_light(); raw_spin_lock_irqsave(&p->pi_lock, flags); #ifdef CONFIG_SMP /* @@ -1644,6 +1654,7 @@ void wake_up_new_task(struct task_struct *p) p->sched_class->task_woken(rq, p); #endif task_rq_unlock(rq, p, &flags); + put_online_cpus_atomic_light(); } #ifdef CONFIG_PREEMPT_NOTIFIERS @@ -2541,6 +2552,7 @@ void sched_exec(void) unsigned long flags; int dest_cpu; + get_online_cpus_atomic_light(); raw_spin_lock_irqsave(&p->pi_lock, flags); dest_cpu = p->sched_class->select_task_rq(p, SD_BALANCE_EXEC, 0); if (dest_cpu == smp_processor_id()) @@ -2550,11 +2562,13 @@ void sched_exec(void) struct migration_arg arg = { p, dest_cpu }; raw_spin_unlock_irqrestore(&p->pi_lock, flags); + put_online_cpus_atomic_light(); stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg); return; } unlock: raw_spin_unlock_irqrestore(&p->pi_lock, flags); + put_online_cpus_atomic_light(); } #endif