From 6f6198a78a34e3d8623f717d05087267e8dedef2 Mon Sep 17 00:00:00 2001 From: Amit Arora <amitarora@in.ibm.com> Date: Wed, 19 May 2010 14:35:57 +0530 Subject: [PATCH] sched: kill migration thread in CPU_POST_DEAD instead of CPU_DEAD [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> --- kernel/sched.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 9990074169fa..ba2d610f4529 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -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); -- 2.34.1