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Commit 5da9a0fb authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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sched: Fix select_task_rq() vs hotplug issues 



Since select_task_rq() is now responsible for guaranteeing
->cpus_allowed and cpu_active_mask, we need to verify this.

select_task_rq_rt() can blindly return
smp_processor_id()/task_cpu() without checking the valid masks,
select_task_rq_fair() can do the same in the rare case that all
SD_flags are disabled.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <20091216170517.961475466@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 38022906

kernel/sched.c

+40 −35
Original line number Diff line number Diff line
@@ -2317,6 +2317,43 @@ void task_oncpu_function_call(struct task_struct *p, 
}



#ifdef CONFIG_SMP

static int select_fallback_rq(int cpu, struct task_struct *p)

{

	int dest_cpu;

	const struct cpumask *nodemask = cpumask_of_node(cpu_to_node(cpu));



	/* Look for allowed, online CPU in same node. */

	for_each_cpu_and(dest_cpu, nodemask, cpu_active_mask)

		if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed))

			return dest_cpu;



	/* Any allowed, online CPU? */

	dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_active_mask);

	if (dest_cpu < nr_cpu_ids)

		return dest_cpu;



	/* No more Mr. Nice Guy. */

	if (dest_cpu >= nr_cpu_ids) {

		rcu_read_lock();

		cpuset_cpus_allowed_locked(p, &p->cpus_allowed);

		rcu_read_unlock();

		dest_cpu = cpumask_any_and(cpu_active_mask, &p->cpus_allowed);



		/*

		 * Don't tell them about moving exiting tasks or

		 * kernel threads (both mm NULL), since they never

		 * leave kernel.

		 */

		if (p->mm && printk_ratelimit()) {

			printk(KERN_INFO "process %d (%s) no "

			       "longer affine to cpu%d\n",

			       task_pid_nr(p), p->comm, cpu);

		}

	}



	return dest_cpu;

}



/*

 * Called from:

 *
@@ -2343,14 +2380,8 @@ int select_task_rq(struct task_struct *p, int sd_flags, int wake_flags) 
	 *   not worry about this generic constraint ]

	 */

	if (unlikely(!cpumask_test_cpu(cpu, &p->cpus_allowed) ||

		     !cpu_active(cpu))) {



		cpu = cpumask_any_and(&p->cpus_allowed, cpu_active_mask);

		/*

		 * XXX: race against hot-plug modifying cpu_active_mask

		 */

		BUG_ON(cpu >= nr_cpu_ids);

	}

		     !cpu_active(cpu)))

		cpu = select_fallback_rq(task_cpu(p), p);



	return cpu;

}
@@ -7319,36 +7350,10 @@ static int __migrate_task_irq(struct task_struct *p, int src_cpu, int dest_cpu) 
static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)

{

	int dest_cpu;

	const struct cpumask *nodemask = cpumask_of_node(cpu_to_node(dead_cpu));



again:

	/* Look for allowed, online CPU in same node. */

	for_each_cpu_and(dest_cpu, nodemask, cpu_active_mask)

		if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed))

			goto move;



	/* Any allowed, online CPU? */

	dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_active_mask);

	if (dest_cpu < nr_cpu_ids)

		goto move;



	/* No more Mr. Nice Guy. */

	if (dest_cpu >= nr_cpu_ids) {

		cpuset_cpus_allowed_locked(p, &p->cpus_allowed);

		dest_cpu = cpumask_any_and(cpu_active_mask, &p->cpus_allowed);



		/*

		 * Don't tell them about moving exiting tasks or

		 * kernel threads (both mm NULL), since they never

		 * leave kernel.

		 */

		if (p->mm && printk_ratelimit()) {

			pr_info("process %d (%s) no longer affine to cpu%d\n",

				task_pid_nr(p), p->comm, dead_cpu);

		}

	}

	dest_cpu = select_fallback_rq(dead_cpu, p);



move:

	/* It can have affinity changed while we were choosing. */

	if (unlikely(!__migrate_task_irq(p, dead_cpu, dest_cpu)))

		goto again;