Re: [PATCH] cpu/hotplug: Allow the CPU in CPU_UP_PREPARE state to be brought up again.

[Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>]

On 2021-11-24 21:17:34 [-0500], Boris Ostrovsky wrote:
> 
> On 11/24/21 5:54 PM, Thomas Gleixner wrote:
> > Any comment from XEN folks?
> 
> 
> If memory allocation in cpu_initialize_context() fails we will not be
> able to bring up the VCPU because xen_cpu_initialized_map bit at the
> top of that routine will already have been set. We will BUG in
> xen_pv_cpu_up() on second (presumably successful) attempt because
> nothing for that VCPU would be initialized. This can in principle be
> fixed by moving allocation to the top of the routine and freeing
> context if the bit in the bitmap is already set.
> 
> 
> Having said that, allocation really should not fail: for PV guests we
> first bring max number of VCPUs up and then offline them down to
> however many need to run. I think if we fail allocation during boot we
> are going to have a really bad day anyway.
> 

So can we keep the patch as-is or are some changes needed?

> -boris

Sebastian