Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 61c7aca6 authored by Wanpeng Li's avatar Wanpeng Li Committed by Ingo Molnar
Browse files

sched/deadline: Fix the intention to re-evalute tick dependency for offline CPU 



The dl task will be replenished after dl task timer fire and start a
new period. It will be enqueued and to re-evaluate its dependency on
the tick in order to restart it. However, if the CPU is hot-unplugged,
irq_work_queue will splash since the target CPU is offline.

As a result we get:

    WARNING: CPU: 2 PID: 0 at kernel/irq_work.c:69 irq_work_queue_on+0xad/0xe0
    Call Trace:
     dump_stack+0x99/0xd0
     __warn+0xd1/0xf0
     warn_slowpath_null+0x1d/0x20
     irq_work_queue_on+0xad/0xe0
     tick_nohz_full_kick_cpu+0x44/0x50
     tick_nohz_dep_set_cpu+0x74/0xb0
     enqueue_task_dl+0x226/0x480
     activate_task+0x5c/0xa0
     dl_task_timer+0x19b/0x2c0
     ? push_dl_task.part.31+0x190/0x190

This can be triggered by hot-unplugging the full dynticks CPU which dl
task is running on.

We enqueue the dl task on the offline CPU, because we need to do
replenish for start_dl_timer(). So, as Juri pointed out, we would
need to do is calling replenish_dl_entity() directly, instead of
enqueue_task_dl(). pi_se shouldn't be a problem as the task shouldn't
be boosted if it was throttled.

This patch fixes it by avoiding the whole enqueue+dequeue+enqueue story, by
first migrating (set_task_cpu()) and then doing 1 enqueue.

Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarWanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luca Abeni <luca.abeni@unitn.it>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1472639264-3932-1-git-send-email-wanpeng.li@hotmail.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent efca03ec

kernel/sched/deadline.c

+18 −28
Original line number Diff line number Diff line
@@ -243,10 +243,8 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq); 
static struct rq *dl_task_offline_migration(struct rq *rq, struct task_struct *p)

{

	struct rq *later_rq = NULL;

	bool fallback = false;



	later_rq = find_lock_later_rq(p, rq);



	if (!later_rq) {

		int cpu;
@@ -254,7 +252,6 @@ static struct rq *dl_task_offline_migration(struct rq *rq, struct task_struct *p 
		 * If we cannot preempt any rq, fall back to pick any

		 * online cpu.

		 */

		fallback = true;

		cpu = cpumask_any_and(cpu_active_mask, tsk_cpus_allowed(p));

		if (cpu >= nr_cpu_ids) {

			/*
@@ -274,16 +271,7 @@ static struct rq *dl_task_offline_migration(struct rq *rq, struct task_struct *p 
		double_lock_balance(rq, later_rq);

	}



	/*

	 * By now the task is replenished and enqueued; migrate it.

	 */

	deactivate_task(rq, p, 0);

	set_task_cpu(p, later_rq->cpu);

	activate_task(later_rq, p, 0);



	if (!fallback)

		resched_curr(later_rq);



	double_unlock_balance(later_rq, rq);



	return later_rq;
@@ -641,29 +629,31 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer) 
		goto unlock;

	}



	enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);

	if (dl_task(rq->curr))

		check_preempt_curr_dl(rq, p, 0);

	else

		resched_curr(rq);



#ifdef CONFIG_SMP

	if (unlikely(!rq->online)) {

		/*

	 * Perform balancing operations here; after the replenishments.  We

	 * cannot drop rq->lock before this, otherwise the assertion in

	 * start_dl_timer() about not missing updates is not true.

	 *

	 * If we find that the rq the task was on is no longer available, we

	 * need to select a new rq.

	 *

	 * XXX figure out if select_task_rq_dl() deals with offline cpus.

		 * If the runqueue is no longer available, migrate the

		 * task elsewhere. This necessarily changes rq.

		 */

	if (unlikely(!rq->online)) {

		lockdep_unpin_lock(&rq->lock, rf.cookie);

		rq = dl_task_offline_migration(rq, p);

		rf.cookie = lockdep_pin_lock(&rq->lock);



		/*

		 * Now that the task has been migrated to the new RQ and we

		 * have that locked, proceed as normal and enqueue the task

		 * there.

		 */

	}

#endif



	enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);

	if (dl_task(rq->curr))

		check_preempt_curr_dl(rq, p, 0);

	else

		resched_curr(rq);



#ifdef CONFIG_SMP

	/*

	 * Queueing this task back might have overloaded rq, check if we need

	 * to kick someone away.