Messages in this thread | | | Date | Mon, 3 Oct 2011 00:50:22 +0200 | From | Frederic Weisbecker <> | Subject | Re: linux-next-20110923: warning kernel/rcutree.c:1833 |
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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?
> if (rdp->cpu != smp_processor_id()) > smp_send_reschedule(rdp->cpu); > else
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