From 5cd038f53ed9ec7a17ab7d536a727363080f4210 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Wed, 4 Jun 2014 16:25:15 +0800 Subject: [PATCH] sched: Migrate waking tasks Current code can fail to migrate a waking task (silently) when TTWU_QUEUE is enabled. When a task is waking, it is pending on the wake_list of the rq, but it is not queued (task->on_rq == 0). In this case, set_cpus_allowed_ptr() and __migrate_task() will not migrate it because its invisible to them. This behavior is incorrect, because the task has been already woken, it will be running on the wrong CPU without correct placement until the next wake-up or update for cpus_allowed. To fix this problem, we need to finish the wakeup (so they appear on the runqueue) before we migrate them. Reported-by: Sasha Levin Reported-by: Jason J. Herne Tested-by: Jason J. Herne Signed-off-by: Lai Jiangshan Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Link: http://lkml.kernel.org/r/538ED7EB.5050303@cn.fujitsu.com Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a814b3c88029..78e5c839df13 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4666,7 +4666,7 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask) goto out; dest_cpu = cpumask_any_and(cpu_active_mask, new_mask); - if (task_on_rq_queued(p)) { + if (task_on_rq_queued(p) || p->state == TASK_WAKING) { struct migration_arg arg = { p, dest_cpu }; /* Need help from migration thread: drop lock and wait. */ task_rq_unlock(rq, p, &flags); @@ -4799,6 +4799,12 @@ static int migration_cpu_stop(void *data) * be on another cpu but it doesn't matter. */ local_irq_disable(); + /* + * We need to explicitly wake pending tasks before running + * __migrate_task() such that we will not miss enforcing cpus_allowed + * during wakeups, see set_cpus_allowed_ptr()'s TASK_WAKING test. + */ + sched_ttwu_pending(); __migrate_task(arg->task, raw_smp_processor_id(), arg->dest_cpu); local_irq_enable(); return 0; -- 2.39.5