Messages in this thread | | | Date | Thu, 23 Jun 2016 13:19:20 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 4/4] sched,fair: Fix PELT integrity for new tasks |
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On Fri, Jun 17, 2016 at 02:01:40PM +0200, Peter Zijlstra wrote: > @@ -8219,6 +8254,19 @@ static int cpu_cgroup_can_attach(struct > if (task->sched_class != &fair_sched_class) > return -EINVAL; > #endif > + /* > + * Serialize against wake_up_new_task() such > + * that if its running, we're sure to observe > + * its full state. > + */ > + raw_spin_unlock_wait(&task->pi_lock); > + /* > + * Avoid calling sched_move_task() before wake_up_new_task() > + * has happened. This would lead to problems with PELT. See > + * XXX. > + */ > + if (task->state == TASK_NEW) > + return -EINVAL; > } > return 0; > }
So I think that's backwards; we want:
if (task->state == TASK_NEW) return -EINVAL; raw_spin_unlock_wait(&task->pi_lock);
Because failing the attach is 'safe', but if we do not observe NEW we must be absolutely sure to observe the full wakeup_new.
But since its not critical I'll change it to more obvious code:
raw_spin_lock_irq(&task->pi_lock); if (task->state == TASK_NEW) ret = -EINVAL; raw_spin_unlock_irq(&task->pi_lock);
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