From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754039AbbIQIGT (ORCPT ); Thu, 17 Sep 2015 04:06:19 -0400 Received: from mail-wi0-f182.google.com ([209.85.212.182]:38358 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753367AbbIQIGH (ORCPT ); Thu, 17 Sep 2015 04:06:07 -0400 Date: Thu, 17 Sep 2015 10:06:02 +0200 From: Ingo Molnar To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Mike Galbraith , Thomas Gleixner , Andrew Morton Subject: [GIT PULL] scheduler fixes Message-ID: <20150917080602.GA23092@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Linus, Please pull the latest sched-urgent-for-linus git tree from: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus # HEAD: 5473e0cc37c03c576adbda7591a6cc8e37c1bb7f sched: 'Annotate' migrate_tasks() A migrate_tasks() locking fix, and a late-coming nohz change plus a nohz debug check. Thanks, Ingo ------------------> Frederic Weisbecker (1): nohz: Assert existing housekeepers when nohz full enabled Vatika Harlalka (1): nohz: Affine unpinned timers to housekeepers Wanpeng Li (1): sched: 'Annotate' migrate_tasks() include/linux/tick.h | 9 +++++++++ kernel/sched/core.c | 36 +++++++++++++++++++++++++++++++----- kernel/time/tick-sched.c | 15 +++++++++++---- 3 files changed, 51 insertions(+), 9 deletions(-) diff --git a/include/linux/tick.h b/include/linux/tick.h index 48d901f83f92..e312219ff823 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -147,11 +147,20 @@ static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) cpumask_or(mask, mask, tick_nohz_full_mask); } +static inline int housekeeping_any_cpu(void) +{ + return cpumask_any_and(housekeeping_mask, cpu_online_mask); +} + extern void tick_nohz_full_kick(void); extern void tick_nohz_full_kick_cpu(int cpu); extern void tick_nohz_full_kick_all(void); extern void __tick_nohz_task_switch(void); #else +static inline int housekeeping_any_cpu(void) +{ + return smp_processor_id(); +} static inline bool tick_nohz_full_enabled(void) { return false; } static inline bool tick_nohz_full_cpu(int cpu) { return false; } static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { } diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8b864ecee0e1..9b786704d34b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -623,18 +623,21 @@ int get_nohz_timer_target(void) int i, cpu = smp_processor_id(); struct sched_domain *sd; - if (!idle_cpu(cpu)) + if (!idle_cpu(cpu) && is_housekeeping_cpu(cpu)) return cpu; rcu_read_lock(); for_each_domain(cpu, sd) { for_each_cpu(i, sched_domain_span(sd)) { - if (!idle_cpu(i)) { + if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) { cpu = i; goto unlock; } } } + + if (!is_housekeeping_cpu(cpu)) + cpu = housekeeping_any_cpu(); unlock: rcu_read_unlock(); return cpu; @@ -5180,24 +5183,47 @@ static void migrate_tasks(struct rq *dead_rq) break; /* - * Ensure rq->lock covers the entire task selection - * until the migration. + * pick_next_task assumes pinned rq->lock. */ lockdep_pin_lock(&rq->lock); next = pick_next_task(rq, &fake_task); BUG_ON(!next); next->sched_class->put_prev_task(rq, next); + /* + * Rules for changing task_struct::cpus_allowed are holding + * both pi_lock and rq->lock, such that holding either + * stabilizes the mask. + * + * Drop rq->lock is not quite as disastrous as it usually is + * because !cpu_active at this point, which means load-balance + * will not interfere. Also, stop-machine. + */ + lockdep_unpin_lock(&rq->lock); + raw_spin_unlock(&rq->lock); + raw_spin_lock(&next->pi_lock); + raw_spin_lock(&rq->lock); + + /* + * Since we're inside stop-machine, _nothing_ should have + * changed the task, WARN if weird stuff happened, because in + * that case the above rq->lock drop is a fail too. + */ + if (WARN_ON(task_rq(next) != rq || !task_on_rq_queued(next))) { + raw_spin_unlock(&next->pi_lock); + continue; + } + /* Find suitable destination for @next, with force if needed. */ dest_cpu = select_fallback_rq(dead_rq->cpu, next); - lockdep_unpin_lock(&rq->lock); rq = __migrate_task(rq, next, dest_cpu); if (rq != dead_rq) { raw_spin_unlock(&rq->lock); rq = dead_rq; raw_spin_lock(&rq->lock); } + raw_spin_unlock(&next->pi_lock); } rq->stop = stop; diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 3319e16f31e5..7c7ec4515983 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -290,16 +290,17 @@ static int __init tick_nohz_full_setup(char *str) __setup("nohz_full=", tick_nohz_full_setup); static int tick_nohz_cpu_down_callback(struct notifier_block *nfb, - unsigned long action, - void *hcpu) + unsigned long action, + void *hcpu) { unsigned int cpu = (unsigned long)hcpu; switch (action & ~CPU_TASKS_FROZEN) { case CPU_DOWN_PREPARE: /* - * If we handle the timekeeping duty for full dynticks CPUs, - * we can't safely shutdown that CPU. + * The boot CPU handles housekeeping duty (unbound timers, + * workqueues, timekeeping, ...) on behalf of full dynticks + * CPUs. It must remain online when nohz full is enabled. */ if (tick_nohz_full_running && tick_do_timer_cpu == cpu) return NOTIFY_BAD; @@ -370,6 +371,12 @@ void __init tick_nohz_init(void) cpu_notifier(tick_nohz_cpu_down_callback, 0); pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n", cpumask_pr_args(tick_nohz_full_mask)); + + /* + * We need at least one CPU to handle housekeeping work such + * as timekeeping, unbound timers, workqueues, ... + */ + WARN_ON_ONCE(cpumask_empty(housekeeping_mask)); } #endif