On Sun, Jul 06, 2014 at 12:20:03AM +0530, pawandeep oza wrote:
> preempt_check_resched would check TIF_NEED_RESCHED
> #define preempt_check_resched() \
> do { \
> if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
> preempt_schedule(); \
> } while (0)
>
> there is a chance that just beofre we disabled irqs, somebody would have
> marked the flag to current, and
> later on, it might happen that, current gets replaced by the process which
> tries to hold a spin_lock which has already been previosuly held by CPU1
> when
> was being plugged out by smp_send_stop.
And preempt_schedule() contains:
/*
* If there is a non-zero preempt_count or interrupts are disabled,
* we do not want to preempt the current task. Just return..
*/
if (likely(!preemptible()))
return;
where preemptible() is defined as:
(preempt_count() == 0 && !irqs_disabled())
which means... if interrupts are disabled (as they are) we don't
return from preempt_schedule() without doing anything.
Scheduling with interrupts disabled is a bug. If you need to add
preempt_disable() before local_irq_disable() to prevent it, then
there's a bug somewhere else, and we don't "fix" that by adding
preempt_disable(). The real bug needs to be found and fixed.
--
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
