On Mon, 2010-05-31 at 22:47 +1000, Nick Piggin wrote:
> > set_current_state(TASK_INTERRUPTIBLE);
> > /*
> > * XXX: what if we are preempted here. No timer is armed. Our state is
> > * TASK_INTERRUPTIBLE, supers_dirty is 1, so no one will ever wake us
> > * up. Thus, we'll sleep forever.
> > */
> > if (supers_dirty)
> > bdi_arm_supers_timer();
> > schedule();
> >
> > Not sure, but I did quick search and it looks like in preemptive kernel,
> > an interrupt may happen in the XXX place above, then it will call
> > 'preempt_schedule_irq()', which sill call 'schedule()'.
>
> Yes, preempt does not participate in tsak sleeping exactly for reasons
> such as this.
>
> From kernel/sched.c:schedule()
>
> if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
> if (unlikely(signal_pending_state(prev->state, prev)))
> prev->state = TASK_RUNNING;
> else
> deactivate_task(rq, prev, DEQUEUE_SLEEP);
> switch_count = &prev->nvcsw;
> }
>
> If the task is not running, then is only removed from the runqueue
> (or reset to running in case of pending signal) IFF it has not been
> scheduled from an involuntary kernel preemption.
>
> So in the XXX region, the task will actually be allowed to run again
> until it calls schedule().
Clear now, thanks a lot again!
--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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