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sched: kill migration thread in CPU_POST_DEAD instead of CPU_DEAD

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[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@in.ibm.com>
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Amit Arora
2010-05-19 14:35:57 +05:30
committed by Greg Kroah-Hartman
parent bd614669ff
commit 6f6198a78a
1 changed files with 13 additions and 3 deletions
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16
kernel/sched.c
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@@ -7752,14 +7752,24 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
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);