[009/123] sched: kill migration thread in CPU_POST_DEAD instead of CPU_DEAD

[Greg KH]

From: Amit Arora <amitarora@xxxxxxxxxx>

[Fixed in a different manner upstream, due to rewrites in this area]

Problem : In a stress test where some heavy tests were running along with
regular CPU offlining and onlining, a hang was observed. The system seems to
be hung at a point where migration_call() tries to kill the migration_thread
of the dying CPU, which just got moved to the current CPU. This migration
thread does not get a chance to run (and die) since rt_throttled is set to 1
on current, and it doesn't get cleared as the hrtimer which is supposed to
reset the rt bandwidth (sched_rt_period_timer) is tied to the CPU which we just
marked dead!

Solution : This patch pushes the killing of migration thread to "CPU_POST_DEAD"
event. By then all the timers (including sched_rt_period_timer) should have got
migrated (along with other callbacks).

Signed-off-by: Amit Arora <amitarora@xxxxxxxxxx>
Signed-off-by: Gautham R Shenoy <ego@xxxxxxxxxx>
Signed-off-by: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
 kernel/sched.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7752,14 +7752,24 @@ migration_call(struct notifier_block *nf
 		cpu_rq(cpu)->migration_thread = NULL;
 		break;
 
+	case CPU_POST_DEAD:
+		/*
+		 * Bring the migration thread down in CPU_POST_DEAD event,
+		 * since the timers should have got migrated by now and thus
+		 * we should not see a deadlock between trying to kill the
+		 * migration thread and the sched_rt_period_timer.
+		 */
+		rq = cpu_rq(cpu);
+		kthread_stop(rq->migration_thread);
+		put_task_struct(rq->migration_thread);
+		rq->migration_thread = NULL;
+		break;
+
 	case CPU_DEAD:
 	case CPU_DEAD_FROZEN:
 		cpuset_lock(); /* around calls to cpuset_cpus_allowed_lock() */
 		migrate_live_tasks(cpu);
 		rq = cpu_rq(cpu);
-		kthread_stop(rq->migration_thread);
-		put_task_struct(rq->migration_thread);
-		rq->migration_thread = NULL;
 		/* Idle task back to normal (off runqueue, low prio) */
 		spin_lock_irq(&rq->lock);
 		update_rq_clock(rq);


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/