linux-kernel - Re: [PATCH tracing/kprobes] kprobes: Disable booster when CONFIG

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Date:	Fri, 29 Jan 2010 18:15:38 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Masami Hiramatsu <mhiramat@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>
Subject: Re: [PATCH tracing/kprobes] kprobes: Disable booster when
 CONFIG_PREEMPT=y

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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