sched/fair: Disable runtime_enabled on dying rq
We kill rq->rd on the CPU_DOWN_PREPARE stage: cpuset_cpu_inactive -> cpuset_update_active_cpus -> partition_sched_domains -> -> cpu_attach_domain -> rq_attach_root -> set_rq_offline This unthrottles all throttled cfs_rqs. But the cpu is still able to call schedule() till take_cpu_down->__cpu_disable() is called from stop_machine. This case the tasks from just unthrottled cfs_rqs are pickable in a standard scheduler way, and they are picked by dying cpu. The cfs_rqs becomes throttled again, and migrate_tasks() in migration_call skips their tasks (one more unthrottle in migrate_tasks()->CPU_DYING does not happen, because rq->rd is already NULL). Patch sets runtime_enabled to zero. This guarantees, the runtime is not accounted, and the cfs_rqs won't exceed given cfs_rq->runtime_remaining = 1, and tasks will be pickable in migrate_tasks(). runtime_enabled is recalculated again when rq becomes online again. Ben Segall also noticed, we always enable runtime in tg_set_cfs_bandwidth(). Actually, we should do that for online cpus only. To prevent races with unthrottle_offline_cfs_rqs() we take get_online_cpus() lock. Reviewed-by: Ben Segall <bsegall@google.com> Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Signed-off-by: Kirill Tkhai <ktkhai@parallels.com> CC: Konstantin Khorenko <khorenko@parallels.com> CC: Paul Turner <pjt@google.com> CC: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1403684382.3462.42.camel@tkhai Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -7817,6 +7817,11 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
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if (period > max_cfs_quota_period)
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return -EINVAL;
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/*
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* Prevent race between setting of cfs_rq->runtime_enabled and
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* unthrottle_offline_cfs_rqs().
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*/
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get_online_cpus();
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mutex_lock(&cfs_constraints_mutex);
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ret = __cfs_schedulable(tg, period, quota);
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if (ret)
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@ -7842,7 +7847,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
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}
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raw_spin_unlock_irq(&cfs_b->lock);
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for_each_possible_cpu(i) {
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for_each_online_cpu(i) {
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struct cfs_rq *cfs_rq = tg->cfs_rq[i];
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struct rq *rq = cfs_rq->rq;
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@ -7858,6 +7863,7 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
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cfs_bandwidth_usage_dec();
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out_unlock:
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mutex_unlock(&cfs_constraints_mutex);
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put_online_cpus();
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return ret;
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}
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@ -3798,6 +3798,19 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
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hrtimer_cancel(&cfs_b->slack_timer);
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}
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static void __maybe_unused update_runtime_enabled(struct rq *rq)
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{
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struct cfs_rq *cfs_rq;
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for_each_leaf_cfs_rq(rq, cfs_rq) {
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struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;
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raw_spin_lock(&cfs_b->lock);
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cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
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raw_spin_unlock(&cfs_b->lock);
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}
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}
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static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
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{
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struct cfs_rq *cfs_rq;
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@ -3811,6 +3824,12 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
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* there's some valid quota amount
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*/
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cfs_rq->runtime_remaining = 1;
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/*
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* Offline rq is schedulable till cpu is completely disabled
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* in take_cpu_down(), so we prevent new cfs throttling here.
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*/
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cfs_rq->runtime_enabled = 0;
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if (cfs_rq_throttled(cfs_rq))
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unthrottle_cfs_rq(cfs_rq);
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}
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@ -3854,6 +3873,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
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return NULL;
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}
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static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
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static inline void update_runtime_enabled(struct rq *rq) {}
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static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}
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#endif /* CONFIG_CFS_BANDWIDTH */
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@ -7362,6 +7382,8 @@ void trigger_load_balance(struct rq *rq)
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static void rq_online_fair(struct rq *rq)
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{
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update_sysctl();
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update_runtime_enabled(rq);
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}
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static void rq_offline_fair(struct rq *rq)
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