On 08/16/2010 03:48 AM, Parmenides wrote:
if (!current_thread_info->preempt_count&& !irqs_disabled()) {
current_thread_info->preempt_count = PREEMPT_ACTIVE;
schedule();
current_thread_info->preempt_count = 0;
}
The if statement checks whether irqs are enabled. If so, the
preemption will be carried out. I wonder why this check is necessary.
Why preemption is prohibited with irqs disabled?
Because the thread you are scheduling to, won't know that
it needs to reenable interrupts.
If interrupts stay disabled "forever", the CPU will not
get any more interrupts, like interrupts that tell it to
reschedule, move the clock forward, etc...
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