From: Thomas Gleixner <t...@linutronix.de>
On CPU unplug tasks which are in a migrate disabled region cannot be pushed
to a different CPU until they returned to migrateable state.
Account the number of tasks on a runqueue which are in a migrate disabled
section and make the hotplug wait mechanism respect that.
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
kernel/sched/core.c | 36 ++++++++++++++++++++++++++++++------
kernel/sched/sched.h | 4 ++++
2 files changed, 34 insertions(+), 6 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1725,10 +1725,17 @@ static void migrate_disable_switch(struc
void migrate_disable(void)
{
- if (current->migration_disabled++)
+ struct task_struct *p = current;
+
+ if (p->migration_disabled) {
+ p->migration_disabled++;
return;
+ }
- barrier();
+ preempt_disable();
+ this_rq()->nr_pinned++;
+ p->migration_disabled = 1;
+ preempt_enable();
}
EXPORT_SYMBOL_GPL(migrate_disable);
@@ -1755,6 +1762,7 @@ void migrate_enable(void)
*/
barrier();
p->migration_disabled = 0;
+ this_rq()->nr_pinned--;
preempt_enable();
}
EXPORT_SYMBOL_GPL(migrate_enable);
@@ -1764,6 +1772,11 @@ static inline bool is_migration_disabled
return p->migration_disabled;
}
+static inline bool rq_has_pinned_tasks(struct rq *rq)
+{
+ return rq->nr_pinned;
+}
+
#endif
/*
@@ -2634,6 +2647,11 @@ static inline bool is_migration_disabled
return false;
}
+static inline bool rq_has_pinned_tasks(struct rq *rq)
+{
+ return false;
+}
+
#endif
static void
@@ -7006,15 +7024,20 @@ static bool balance_push(struct rq *rq)
* Both the cpu-hotplug and stop task are in this case and are
* required to complete the hotplug process.
*/
- if (is_per_cpu_kthread(push_task)) {
+ if (is_per_cpu_kthread(push_task) || is_migration_disabled(push_task)) {
/*
* If this is the idle task on the outgoing CPU try to wake
* up the hotplug control thread which might wait for the
* last task to vanish. The rcuwait_active() check is
* accurate here because the waiter is pinned on this CPU
* and can't obviously be running in parallel.
+ *
+ * On RT kernels this also has to check whether there are
+ * pinned and scheduled out tasks on the runqueue. They
+ * need to leave the migrate disabled section first.
*/
- if (!rq->nr_running && rcuwait_active(&rq->hotplug_wait)) {
+ if (!rq->nr_running && !rq_has_pinned_tasks(rq) &&
+ rcuwait_active(&rq->hotplug_wait)) {
raw_spin_unlock(&rq->lock);
rcuwait_wake_up(&rq->hotplug_wait);
raw_spin_lock(&rq->lock);
@@ -7063,7 +7086,8 @@ static void balance_hotplug_wait(void)
{
struct rq *rq = this_rq();
- rcuwait_wait_event(&rq->hotplug_wait, rq->nr_running == 1,
+ rcuwait_wait_event(&rq->hotplug_wait,
+ rq->nr_running == 1 && !rq_has_pinned_tasks(rq),
TASK_UNINTERRUPTIBLE);
}
@@ -7310,7 +7334,7 @@ int sched_cpu_dying(unsigned int cpu)
sched_tick_stop(cpu);
rq_lock_irqsave(rq, &rf);
- BUG_ON(rq->nr_running != 1);
+ BUG_ON(rq->nr_running != 1 || rq_has_pinned_tasks(rq));
rq_unlock_irqrestore(rq, &rf);
calc_load_migrate(rq);
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1053,6 +1053,10 @@ struct rq {
/* Must be inspected within a rcu lock section */
struct cpuidle_state *idle_state;
#endif
+
+#if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP)
+ unsigned int nr_pinned;
+#endif
};
#ifdef CONFIG_FAIR_GROUP_SCHED
