Commit efc30814 authored by Kirill Korotaev's avatar Kirill Korotaev Committed by Linus Torvalds
Browse files

[PATCH] sched: CPU hotplug race vs. set_cpus_allowed() 



There is a race between set_cpus_allowed() and move_task_off_dead_cpu().
__migrate_task() doesn't report any err code, so task can be left on its
runqueue if its cpus_allowed mask changed so that dest_cpu is not longer a
possible target.  Also, chaning cpus_allowed mask requires rq->lock being
held.

Signed-off-by: default avatarKirill Korotaev <dev@openvz.org>
Acked-By: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent cc94abfc

kernel/sched.c

+14 −4
Original line number Diff line number Diff line
@@ -4412,13 +4412,16 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed); 
 *

 * So we race with normal scheduler movements, but that's OK, as long

 * as the task is no longer on this CPU.

 *

 * Returns non-zero if task was successfully migrated.

 */

static void __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)

static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)

{

	runqueue_t *rq_dest, *rq_src;

	int ret = 0;



	if (unlikely(cpu_is_offline(dest_cpu)))

		return;

		return ret;



	rq_src = cpu_rq(src_cpu);

	rq_dest = cpu_rq(dest_cpu);
@@ -4446,9 +4449,10 @@ static void __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) 
		if (TASK_PREEMPTS_CURR(p, rq_dest))

			resched_task(rq_dest->curr);

	}



	ret = 1;

out:

	double_rq_unlock(rq_src, rq_dest);

	return ret;

}



/*
@@ -4518,9 +4522,12 @@ wait_to_die: 
/* Figure out where task on dead CPU should go, use force if neccessary. */

static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk)

{

	runqueue_t *rq;

	unsigned long flags;

	int dest_cpu;

	cpumask_t mask;



restart:

	/* On same node? */

	mask = node_to_cpumask(cpu_to_node(dead_cpu));

	cpus_and(mask, mask, tsk->cpus_allowed);
@@ -4532,8 +4539,10 @@ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk) 


	/* No more Mr. Nice Guy. */

	if (dest_cpu == NR_CPUS) {

		rq = task_rq_lock(tsk, &flags);

		cpus_setall(tsk->cpus_allowed);

		dest_cpu = any_online_cpu(tsk->cpus_allowed);

		task_rq_unlock(rq, &flags);



		/*

		 * Don't tell them about moving exiting tasks or
@@ -4545,7 +4554,8 @@ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk) 
			       "longer affine to cpu%d\n",

			       tsk->pid, tsk->comm, dead_cpu);

	}

	__migrate_task(tsk, dead_cpu, dest_cpu);

	if (!__migrate_task(tsk, dead_cpu, dest_cpu))

		goto restart;

}



/*

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