Re: [RFC PATCH 07/13] sched: Add core wide task selection and scheduling.

[Chen Yu]

On Wed, Mar 04, 2020 at 04:59:57PM +0000, vpillai wrote:
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> 
> Instead of only selecting a local task, select a task for all SMT
> siblings for every reschedule on the core (irrespective which logical
> CPU does the reschedule).
> 
> There could be races in core scheduler where a CPU is trying to pick
> a task for its sibling in core scheduler, when that CPU has just been
> offlined.  We should not schedule any tasks on the CPU in this case.
> Return an idle task in pick_next_task for this situation.
> 
> NOTE: there is still potential for siblings rivalry.
> NOTE: this is far too complicated; but thus far I've failed to
>       simplify it further.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Julien Desfossez <jdesfossez@xxxxxxxxxxxxxxxx>
> Signed-off-by: Vineeth Remanan Pillai <vpillai@xxxxxxxxxxxxxxxx>
> Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> ---
[cut]

Hi Vineeth,
An NULL pointer exception was found when testing V5 on top of stable
v5.6.2. And we tried the patch Peter suggested, the NULL pointer
was not found so far. We don't know if this change would help mitigate
the symptom, but it should do no harm to test with this fix applied.

Thanks,
Chenyu