Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:
 "Three CPU hotplug related fixes and a debugging improvement"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/debug: Add debugfs knob for "sched_debug"
  sched/core: WARN() when migrating to an offline CPU
  sched/fair: Plug hole between hotplug and active_load_balance()
  sched/fair: Avoid newidle balance for !active CPUs

5 files changed, 25 insertions, 3 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 136a76d80dbf..18a6966567da 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1173,6 +1173,10 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
         WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
                                       lockdep_is_held(&task_rq(p)->lock)));
 #endif
+        /*
+         * Clearly, migrating tasks to offline CPUs is a fairly daft thing.
+         */
+        WARN_ON_ONCE(!cpu_online(new_cpu));
 #endif
 
         trace_sched_migrate_task(p, new_cpu);
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 8e536d963652..01217fb5a5de 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -181,11 +181,16 @@ static const struct file_operations sched_feat_fops = {
         .release        = single_release,
 };
 
+__read_mostly bool sched_debug_enabled;
+
 static __init int sched_init_debug(void)
 {
         debugfs_create_file("sched_features", 0644, NULL, NULL,
                         &sched_feat_fops);
 
+        debugfs_create_bool("sched_debug", 0644, NULL,
+                        &sched_debug_enabled);
+
         return 0;
 }
 late_initcall(sched_init_debug);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0a85641e62ce..70ba32e08a23 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8437,6 +8437,12 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
         this_rq->idle_stamp = rq_clock(this_rq);
 
         /*
+         * Do not pull tasks towards !active CPUs...
+         */
+        if (!cpu_active(this_cpu))
+                return 0;
+
+        /*
          * This is OK, because current is on_cpu, which avoids it being picked
          * for load-balance and preemption/IRQs are still disabled avoiding
          * further scheduler activity on it and we're being very careful to
@@ -8543,6 +8549,13 @@ static int active_load_balance_cpu_stop(void *data)
         struct rq_flags rf;
 
         rq_lock_irq(busiest_rq, &rf);
+        /*
+         * Between queueing the stop-work and running it is a hole in which
+         * CPUs can become inactive. We should not move tasks from or to
+         * inactive CPUs.
+         */
+        if (!cpu_active(busiest_cpu) || !cpu_active(target_cpu))
+                goto out_unlock;
 
         /* make sure the requested cpu hasn't gone down in the meantime */
         if (unlikely(busiest_cpu != smp_processor_id() ||
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 746ac78ff492..14db76cd496f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1951,6 +1951,8 @@ extern struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq);
 extern struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq);
 
 #ifdef  CONFIG_SCHED_DEBUG
+extern bool sched_debug_enabled;
+
 extern void print_cfs_stats(struct seq_file *m, int cpu);
 extern void print_rt_stats(struct seq_file *m, int cpu);
 extern void print_dl_stats(struct seq_file *m, int cpu);
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 5d0062cc10cb..f1cf4f306a82 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -14,11 +14,9 @@ cpumask_var_t sched_domains_tmpmask2;
 
 #ifdef CONFIG_SCHED_DEBUG
 
-static __read_mostly int sched_debug_enabled;
-
 static int __init sched_debug_setup(char *str)
 {
-        sched_debug_enabled = 1;
+        sched_debug_enabled = true;
 
         return 0;
 }