Re: [Qemu-devel] [FIX PATCH] spapr: Gracefully fail CPU thread unplug

[Bharata B Rao]

On Thu, Aug 18, 2016 at 10:57:04AM +1000, David Gibson wrote:
> On Wed, Aug 17, 2016 at 07:31:38PM +0530, Bharata B Rao wrote:
> > sPAPR supports only Core level CPU plug and unplug, but nothing
> > prevents user from issuing a device_del on the underlying thread
> > device by using its qom path directly. This hits g_assert(hotplug_ctrl)
> > in qdev_unplug().
> > 
> > Gracefully reject such unplug requests from ->unplug() handler
> > 
> > Reported-by: Shivaprasad G Bhat <address@hidden>
> > Signed-off-by: Bharata B Rao <address@hidden>
> 
> Why isn't there a graceful failure if we return NULL from the
> hotplug_handler()?  Doesn't that indicate a bug in the generic code?
> Couldn't the same error be triggered by attempting to unplug some
> other random device - say the RTC on x86, or the NVRAM on POWER?

True, realized that this error can be triggered for other devices as well
like dr-connector or icp devices. So it definitely doesn't make sense
to explicitly return a non-NULL hotplug_handler for all of these
and then fail the unplug gracefully from ->unplug() like I am doing here
for CPU thread devices.

Hence, this particular fix isn't needed right now. May be we can gracefully
error out for all such cases from qdev_unplug().

Regards,
Bharata.