On 2011-01-31 14:22, Avi Kivity wrote: > On 01/31/2011 01:27 PM, Jan Kiszka 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. > > If we use signalfd() (either kernel provided or thread+pipe), we kick > out of select by select()ing it (though I don't see how it works without > an iothread, since an fd can't stop a vcpu unless you enable SIGIO on > it, which is silly for signalfd) > > If you leave it as a naked signal, then it can break out of either > pselect() or vcpu. > > Since the goal is to drop !CONFIG_IOTHREAD, the first path seems better, > I just don't understand the problem with emulated signalfd(). > With the emulated signalfd, there won't be any signal for the VCPU while in KVM_RUN. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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
