sched: Ensure the migration task doesn't go away during use

Like sched_migrate_task(), set_cpus_allowed_ptr() should hold
onto the migration thread too.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 475138c42548f0f8de664d2a77b0bb13ce52efa8..7f83be35d65c623ff3f15670cc73f444019fc33e 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7078,8 +7078,12 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
 
        if (migrate_task(p, cpumask_any_and(cpu_online_mask, new_mask), &req)) {
                /* Need help from migration thread: drop lock and wait. */
+               struct task_struct *mt = rq->migration_thread;
+
+               get_task_struct(mt);
                task_rq_unlock(rq, &flags);
                wake_up_process(rq->migration_thread);
+               put_task_struct(mt);
                wait_for_completion(&req.done);
                tlb_migrate_finish(p->mm);
                return 0;