On 11/14/2011 12:01 PM, Alexander Graf wrote: > > On 14.11.2011, at 18:22, Scott Wood <scottwood@xxxxxxxxxxxxx> wrote: > >> kvmppc_core_check_exceptions can clear MSR_WE, so we need to check after >> that. We can't enable interrupts after kvmppc_core_check_exceptions (or >> rather, if we do, we need to check again once interrupts are >> re-disabled, as in the MSR_WE case) because otherwise we could have an >> exception delivered afterward and receive the resched IPI at just the >> wrong time to take any action on it (just like the signal check). > > Well, but if you enable interrupts here you're basically rendering code that runs earlier in disabled-interrupt mode racy. That's why once we wake, we disable interrupts and check again. > How does this align with the signal handling? We could receive a signal here and not handle it the same as the race you fixed earlier, no? Signals are checked by the caller after calling prepare_to_enter. Moving the check into prepare_to_enter wouldn't buy us much since the method of returning is different, and so there'd still need to be code in the caller to deal with it. -Scott -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
