[PATCH] migration_thread() race fix

From: Srivatsa Vaddagiri <vatsa@in.ibm.com>

Noticed that migration_thread can examine "kthread_should_stop()?" without
setting its state to TASK_INTERRUPTIBLE first.  This can cause kthread_stop
on that thread to block forever ...

P.S 	- I assumed that having the task state set to TASK_INTERRUTIBLE
	  while it is doing active_load_balance is fine. It seemed to be
	  the case earlier also.

diff --git a/kernel/sched.c b/kernel/sched.c
index 422bfeb614e1eee4b259b96652af41fd479e3b94..d083166dd3f0a6f3804d191d48305156171b4d28 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3372,6 +3372,7 @@ static int migration_thread(void * data)
        rq = cpu_rq(cpu);
        BUG_ON(rq->migration_thread != current);
 
+       set_current_state(TASK_INTERRUPTIBLE);
        while (!kthread_should_stop()) {
                struct list_head *head;
                migration_req_t *req;
@@ -3393,10 +3394,10 @@ static int migration_thread(void * data)
 
                head = &rq->migration_queue;
 
-               current->state = TASK_INTERRUPTIBLE;
                if (list_empty(head)) {
                        spin_unlock_irq(&rq->lock);
                        schedule();
+                       set_current_state(TASK_INTERRUPTIBLE);
                        continue;
                }
                req = list_entry(head->next, migration_req_t, list);
@@ -3417,6 +3418,7 @@ static int migration_thread(void * data)
 
                complete(&req->done);
        }
+       __set_current_state(TASK_RUNNING);
        return 0;
 
 wait_to_die: