On Mon, Jan 31, 2011 at 11:27 AM, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: > On 2011-01-31 11:03, Avi Kivity wrote: >> On 01/27/2011 04:33 PM, Jan Kiszka wrote: >>> Found by Stefan Hajnoczi: There is a race in kvm_cpu_exec between >>> checking for exit_request on vcpu entry and timer signals arriving >>> before KVM starts to catch them. Plug it by blocking both timer related >>> signals also on !CONFIG_IOTHREAD and process those via signalfd. >>> >>> As this fix depends on real signalfd support (otherwise the timer >>> signals only kick the compat helper thread, and the main thread hangs), >>> we need to detect the invalid constellation and abort configure. >>> >>> Signed-off-by: Jan Kiszka<jan.kiszka@xxxxxxxxxxx> >>> CC: Stefan Hajnoczi<stefanha@xxxxxxxxxxxxxxxxxx> >>> --- >>> >>> I don't want to invest that much into !IOTHREAD anymore, so let's see if >>> the proposed catch&abort is acceptable. >>> >> >> I don't understand the dependency on signalfd. The normal way of doing >> things, either waiting for the signal in sigtimedwait() or in >> ioctl(KVM_RUN), works with SIGALRM just fine. > > And how would you be kicked out of the select() call if it is waiting > with a timeout? We only have a single thread here. > > The only alternative is Stefan's original proposal. But that required > fiddling with the signal mask twice per KVM_RUN. I think my original patch messed with the sigmask in the wrong place, as you mentioned doing it twice per KVM_RUN isn't a good idea. I wonder if we can enable SIGALRM only in blocking calls and guest code execution but without signalfd. It might be possible, I don't see an immediate problem with doing that, we might have to use pselect(2) or similar in a few places. Stefan -- 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
