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().
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