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    SubjectRe: linux-next-20110923: warning kernel/rcutree.c:1833
    On Mon, Oct 03, 2011 at 12:50:22AM +0200, Frederic Weisbecker wrote:
    > On Fri, Sep 30, 2011 at 12:24:38PM -0700, Paul E. McKenney wrote:
    > > @@ -328,11 +326,11 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
    > > return 1;
    > > }
    > >
    > > - /* If preemptible RCU, no point in sending reschedule IPI. */
    > > - if (rdp->preemptible)
    > > - return 0;
    > > -
    > > - /* The CPU is online, so send it a reschedule IPI. */
    > > + /*
    > > + * The CPU is online, so send it a reschedule IPI. This forces
    > > + * it through the scheduler, and (inefficiently) also handles cases
    > > + * where idle loops fail to inform RCU about the CPU being idle.
    > > + */
    >
    > If the idle loop forgets to call rcu_idle_enter() before going to
    > sleep, I don't know if it's a good idea to try to cure that situation
    > by forcing a quiescent state remotely. It may make the thing worse
    > because we actually won't notice the lack of call to rcu_idle_enter()
    > that the rcu stall detector would otherwise report to us.
    >
    > Also I don't think that works. If the task doesn't have
    > TIF_RESCHED, it won't go through the scheduler on irq exit.
    > smp_send_reschedule() doesn't set the flag. And also scheduler_ipi()
    > returns right away if no wake up is pending.
    >
    > So, other than resuming the idle loop to sleep again, nothing may happen.
    >
    > Or am I missing something?

    Hmmm... Seems like the IPIs aren't helping in any case, then?

    I suppose that I could do an smp_call_function_single(), which then
    did a set_need_resched()...

    But this is a separate issue that I need to deal with. That said, any
    suggestions are welcome!

    Thanx, Paul

    > > if (rdp->cpu != smp_processor_id())
    > > smp_send_reschedule(rdp->cpu);
    > > else



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