On Thu, Jul 23, 2020 at 01:14:10PM +0300, Nikolay Shirokovskiy wrote:
> We are dropping the only reference here so that the event loop thread
> is going to be exited synchronously. In order to avoid deadlocks we
> need to unlock the VM so that any handler being called can finish
> execution and thus even loop thread be finished too.
>
> Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy@xxxxxxxxxxxxx>
> ---
> src/qemu/qemu_domain.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index 5b22eb2..82b3d11 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -1637,11 +1637,21 @@ void
> qemuDomainObjStopWorker(virDomainObjPtr dom)
> {
> qemuDomainObjPrivatePtr priv = dom->privateData;
> + virEventThread *eventThread;
>
> - if (priv->eventThread) {
> - g_object_unref(priv->eventThread);
> - priv->eventThread = NULL;
> - }
> + if (!priv->eventThread)
> + return;
> +
> + /*
> + * We are dropping the only reference here so that the event loop thread
> + * is going to be exited synchronously. In order to avoid deadlocks we
> + * need to unlock the VM so that any handler being called can finish
> + * execution and thus even loop thread be finished too.
> + */
> + eventThread = g_steal_pointer(&priv->eventThread);
> + virObjectUnlock(dom);
> + g_object_unref(eventThread);
> + virObjectLock(dom);
Hmm, I'm really not at all comfortable with this. I don't have confidence
that qemuProcessStop() safe if we drpo & reacquire the lock half way
through its cleanup process. The 'virDomainObj' is in a semi-clean
state, 1/2 running 1/2 shutoff.
This is the key reason I think I didn't do the synchronous thread join
in the event loop.
Regards,
Daniel
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