Messages in this thread | | | Date | Sat, 5 Jul 2014 20:25:33 +0100 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH] machine_power_off: not only local_irq_disable but also do disable preemption |
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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.
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