On Tue, Nov 27, 2012 at 05:48:18PM +0100, Frederic Weisbecker wrote: > 2012/11/27 Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>: > > On Tue, Nov 27, 2012 at 04:56:30PM +0100, Frederic Weisbecker wrote: > >> 2012/11/27 Gleb Natapov <gleb@xxxxxxxxxx>: > >> > For KVM_PV_REASON_PAGE_NOT_PRESENT it behaves like an exception. > >> > >> Ok. > >> There seem to be a bug in kvm_async_pf_task_wait(). Using > >> idle_cpu(cpu) to find out if the current task is the idle task may not > >> work if there is pending wake up. Me may schedule another task but > >> when that other task sleeps later we can't schedule back to idle until > >> the fault is completed. > >> > >> The right way is to use is_idle_task(current) > > > > Agreed. But if you instead need to figure out whether or not RCU believes > > that the CPU is idle, use rcu_is_cpu_idle(). You need to figure out > > whether or not RCU believes that the CPU is idle if you are trying to > > play fast and loose with rcu_irq_enter() and rcu_irq_exit(). > > Right. I was referring to another problem though. They don't want to > schedule on the following cases: > > 1) preemption disabled, of course. > 3) we are in the idle task. Because if we want to sleep in order to > wait for the page fault completion, we need to be able to schedule the > idle task. But we are already the idle task. > > Now idle_cpu(cpu) is the wrong check for that. Fair enough! ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
