[PATCH v3 1/2] drm/sched: Avoid job cleanup if sched thread is parked.

[Andrey Grodzovsky]

On 11/26/19 4:08 AM, Christian König wrote:
> Am 25.11.19 um 17:51 schrieb Steven Price:
>> On 25/11/2019 14:10, Andrey Grodzovsky wrote:
>>> When the sched thread is parked we assume ring_mirror_list is
>>> not accessed from here.
>> FWIW I don't think this is necessary. kthread_park() will wait until the
>> thread is parked, at which point the thread is stuck in kthread_parkme()
>> until unparked.
>>
>> So all this does is avoid waiting for any cleanup jobs before parking -
>> which might be a reasonable goal in itself, but if so lets at least
>> document that.
>
> Now that you mention it that is indeed wrong.


I wouldn't s call it wrong but superfluous in current code as indeed 
once the thread is parked there will be no subsequent calls to 
drm_sched_get_cleanup_job until the thread is unpacked back, if for 
example we decide to call drm_sched_get_cleanup_job from a work item 
which keeps scheduled it would be needed.


>
> The real problem is that in the main thread we mangled the call to 
> kthread_parkme() into drm_sched_blocked() which can be called in 
> atomic context.


Where is the atomic context in wait_event_interruptible ? I seem no to 
see any.

Andrey


>
> I suggest to rework this so that the kthread_should_park() and 
> kthread_should_stop() test in wait_event_interruptible() come first 
> and then call kthread_parkme() outside of the wait_event_interruptible().
>
> Regards,
> Christian.
>
>>
>> Steve
>>
>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
>>> Reviewed-by: Christian König <christian.koenig at amd.com>
>>> ---
>>>   drivers/gpu/drm/scheduler/sched_main.c | 10 +++++++---
>>>   1 file changed, 7 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c 
>>> b/drivers/gpu/drm/scheduler/sched_main.c
>>> index d4cc728..6774955 100644
>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>> @@ -635,9 +635,13 @@ drm_sched_get_cleanup_job(struct 
>>> drm_gpu_scheduler *sched)
>>>       struct drm_sched_job *job;
>>>       unsigned long flags;
>>>   -    /* Don't destroy jobs while the timeout worker is running */
>>> -    if (sched->timeout != MAX_SCHEDULE_TIMEOUT &&
>>> -        !cancel_delayed_work(&sched->work_tdr))
>>> +    /*
>>> +    * Don't destroy jobs while the timeout worker is running OR thread
>>> +    * is being parked and hence assumed to not touch ring_mirror_list
>>> +    */
>>> +    if ((sched->timeout != MAX_SCHEDULE_TIMEOUT &&
>>> +         !cancel_delayed_work(&sched->work_tdr)) ||
>>> +         __kthread_should_park(sched->thread))
>>>           return NULL;
>>>         spin_lock_irqsave(&sched->job_list_lock, flags);
>>>
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