# Re: \[Xen-devel\] \[PATCH 05/27\] xen, cpu hotplug: Don't call cpu\_bringup() in xen\_play\_dead()

- From: Jan Beulich \<hidden\>
- Date: 2012-06-01 15:36:36 
- List: linux-arch
- Page: https://ratatoskr.run/linux-arch/2012/06/3873285
- Thread: https://ratatoskr.run/linux-arch/2012/06/3873118/t.md

```text
>>> On 01.06.12 at 17:13, "Srivatsa S. Bhat" [ref]
wrote:
> On 06/01/2012 06:29 PM, Jan Beulich wrote:
> 
>>>>> On 01.06.12 at 11:11, "Srivatsa S. Bhat" [ref]
>> wrote:
>>> xen_play_dead calls cpu_bringup() which looks weird, because xen_play_dead()
>>> is invoked in the cpu down path, whereas cpu_bringup() (as the name 
>>> suggests) is useful in the cpu bringup path.
>> 
>> This might not be correct - the code as it is without this change is
>> safe even when the vCPU gets onlined back later by an external
>> entity (e.g. the Xen tool stack), and it would in that case resume
>> at the return point of the VCPUOP_down hypercall. That might
>> be a heritage from the original XenoLinux tree though, and be
>> meaningless in pv-ops context - Jeremy, Konrad?
>> 
>> Possibly it was bogus/unused even in that original tree - Keir?
>>
> 
> 
> Thanks for your comments Jan!
> 
> In case this change is wrong, the other method I had in mind was to call
> cpu_bringup_and_idle() in xen_play_dead(). (Even ARM does something similar,
> in the sense that it runs the cpu bringup code including cpu_idle(), in the
> cpu offline path, namely the cpu_die() function). Would that approach work
> for xen as well? If yes, then we wouldn't have any issues to convert xen to
> generic code.

No, that wouldn't work either afaict - the function is expected
to return.

Jan
```