Re: [PATCH] sched: fix scheduler_disable() with core scheduling

[Sergey Dyasli <sergey.dyasli@citrix.com>]

(CC Igor)

On 09/04/2020 13:50, Jürgen Groß wrote:
> On 09.04.20 11:41, Sergey Dyasli wrote:
>> In core-scheduling mode, Xen might crash when entering ACPI S5 state.
>> This happens in sched_slave() during is_idle_unit(next) check because
>> next->vcpu_list is stale and points to an already freed memory.
>>
>> This situation happens shortly after scheduler_disable() is called if
>> some CPU is still inside sched_slave() softirq. Current logic simply
>> returns prev->next_task from sched_wait_rendezvous_in() which causes
>> the described crash because next_task->vcpu_list has become invalid.
>>
>> Fix the crash by returning NULL from sched_wait_rendezvous_in() in
>> the case when scheduler_disable() has been called.
>>
>> Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
> 
> Good catch!
> 
> Have you seen any further problems (e.g. with cpu on/offlining) with
> this patch applied?

This patch shouldn't affect cpu on/offlining AFAICS. Igor was the one testing
cpu on/offlining and I think he came to a conclusion that it's broken even
without core-scheduling enabled.

> Reviewed-by: Juergen Gross <jgross@suse.com>

Thanks!

--
Sergey