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>

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 475138c42548..7f83be35d65c 100644
--- 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;