Re: [PATCH v1] xen/sched/null: avoid crash after failed domU creation

[Jan Beulich <jbeulich@suse.com>]

On 18.05.2023 23:27, Stewart Hildebrand wrote:
> On 5/5/23 01:59, Juergen Gross wrote:
>> On 01.05.23 22:30, Stewart Hildebrand wrote:
>>> When creating a domU, but the creation fails, there is a corner case that may
>>> lead to a crash in the null scheduler when running a debug build of Xen.
>>>
>>> (XEN) ****************************************
>>> (XEN) Panic on CPU 0:
>>> (XEN) Assertion 'npc->unit == unit' failed at common/sched/null.c:379
>>> (XEN) ****************************************
>>>
>>> The events leading to the crash are:
>>>
>>> * null_unit_insert() was invoked with the unit offline. Since the unit was
>>>    offline, unit_assign() was not called, and null_unit_insert() returned.
>>> * Later during domain creation, the unit was onlined
>>> * Eventually, domain creation failed due to bad configuration
>>> * null_unit_remove() was invoked with the unit still online. Since the unit was
>>>    online, it called unit_deassign() and triggered an ASSERT.
>>>
>>> To fix this, only call unit_deassign() when npc->unit is non-NULL in
>>> null_unit_remove.
>>>
>>> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
>>
>> Reviewed-by: Juergen Gross <jgross@suse.com>
> 
> Thanks for the review. Does this still need a maintainer ack?

In principle yes. I might be willing to time out at some point, but
not before at least one ping was sent (and some more time has passed
afterwards).

Jan