[Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD

[Avi Kivity]

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<address@hidden>
> CC: Stefan Hajnoczi<address@hidden>
> ---
>
> 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.

--
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