On torsdagen den 4 april 2002 21.26, Robert Love wrote:
> On Thu, 2002-04-04 at 14:14, Linus Torvalds wrote:
> > The answer is that preempt_schedule() illegally sets
> >
> > current->state = TASK_RUNNING;
> >
> > without asking the process whether that's OK. The SMP code never does
> > anything like that.
>
> Well Ingo added that ;)
>
> We used to just set a flag in the preempt_count that marked the task as
> preempted and made sure on its next trip into schedule it ran again.
>
How about doing:
asmlinkage void preempt_schedule(void)
{
unsigned long saved_state;
if (unlikely(preempt_get_count()))
return;
preempt_disable(); /* or use an atomic operation */
saved_state = current->state;
current->state = TASK_RUNNING;
preempt_enable_no_resched(); /* we are scheduling anyway... */
schedule();
current->state = saved_state;
}
It is unlikely to get preemption between schedule() and the
setting since schedule it self checks - the window is small.
And when it hits if will correctly restore the correct value.
Note this code does not need to solve the FLAG problem.
current->state |= FLAG
* PREEMPT *
current->state |= FLAG
schedule()
current->state &= ~FLAG
schedule() with flag disabled
/RogerL
-- Roger Larsson Skellefteċ Sweden- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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