On Fri, Sep 04, 2020 at 05:46:18PM +0100, Daniel P. Berrangé wrote:
> 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.
Hmm, I see your justification in the other reply now.
Reviewed-by: Daniel P. Berrangé <berrange@xxxxxxxxxx>
Regards,
Daniel
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