Re: [PATCH tracing/kprobes] kprobes: Disable booster whenCONFIG_PREEMPT=y

[Peter Zijlstra]

On Fri, 2010-01-29 at 12:08 -0500, Mathieu Desnoyers wrote:
> 
> If a task is set as stopped, and the preempted before calling schedule,
> can this result in a preempted task staying in that state for an
> arbitrary long period of time ? Or is there some mechanism prohibiting
> that in the scheduler ? 

PREEMPT_ACTIVE does that:

preempt_schedule()
                add_preempt_count(PREEMPT_ACTIVE);
                schedule();


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, 1);
                switch_count = &prev->nvcsw;
        }


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