drm_sched with panfrost crash on T820

[Neil Armstrong]

Hi Steven,

On 27/09/2019 17:00, Steven Price wrote:
> On 27/09/2019 12:48, Neil Armstrong wrote:
>> Hi,
>>
>> On 27/09/2019 13:27, Neil Armstrong wrote:
>>> Hi Steven,
>>>
>>> Thanks for your prompt reaction !
>>>
>>> On 27/09/2019 12:48, Steven Price wrote:
>>>> On 27/09/2019 10:55, Steven Price wrote:
>>>> [...]
>>>>> One obvious issue with the DRM scheduler is that there is a call to
>>>>> cancel_delayed_work() in drm_sched_stop() which to me looks like it
>>>>> should be cancel_delayed_work_sync() to ensure that the timeout handling
>>>>> has completed.
>>>>>
>>>>> However in the above scenario a _sync() variety would then cause a
>>>>> deadlock (one thread has pfdev->reset_lock and is waiting for the other
>>>>> thread which is trying to take the lock).
>>>>>
>>>>> So we need to update Panfrost so that it can coordinate the reset
>>>>> between schedulers. Can you try something like the following (untested):
>>>>
>>>> And actually testing it I of course discover it doesn't quite work. We
>>>> do need the cancel_delayed_work_sync() in the DRM scheduler (when
>>>> stopping a different scheduler) and we need to avoid holding the
>>>> reset_lock during the drm_sched_stop() call to prevent deadlocking with
>>>> another thread handling a timeout.
>>>
>>> Yep the first patch wasn't fixing the issue all the time.
>>>
>>>>
>>>> Can you give the following patch a spin? I don't have a great
>>>> reproduction case, so it would be good to get some confidence it fixes
>>>> the problem.
>>>

[...]

I ran 15 jobs with your patch and none failed, so you can add my:
Tested-by: Neil Armstrong <narmstrong at baylibre.com>

No idea how this drm_sched_start() failure came, but I wasn't able
to reproduce it at all...

Thanks,
Neil

> 
> Steve
> 
>> Neil
>>>
>>> Thanks,
>>> Neil
>>>
>>>>
>>>> ----8<----
>>>> From 521a286789260197ae94f698932ebf369efc45ad Mon Sep 17 00:00:00 2001
>>>> From: Steven Price <steven.price at arm.com>
>>>> Date: Fri, 27 Sep 2019 11:42:40 +0100
>>>> Subject: [PATCH] drm/panfrost: Handle resetting on timeout better
>>>>
>>>> Panfrost uses multiple schedulers (one for each slot, so 2 in reality),
>>>> and on a timeout has to stop all the schedulers to safely perform a
>>>> reset. However more than one scheduler can trigger a timeout at the same
>>>> time. This race condition results in jobs being freed while they are
>>>> still in use.
>>>>
>>>> Modify drm_sched_stop() to call cancel_delayed_work_sync() when stopping
>>>> a different scheduler to the one belonging to the passed in job.
>>>> panfrost_job_timedout() is also modified to only allow one thread at a
>>>> time to handle the reset. Any subsequent threads simply return assuming
>>>> that the first thread will handle the situation.
>>>>
>>>> Signed-off-by: Steven Price <steven.price at arm.com>
>>>> ---
>>>>  drivers/gpu/drm/panfrost/panfrost_device.h |  2 ++
>>>>  drivers/gpu/drm/panfrost/panfrost_job.c    | 11 ++++++++++-
>>>>  drivers/gpu/drm/scheduler/sched_main.c     |  5 ++++-
>>>>  3 files changed, 16 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
>>>> index f503c566e99f..6441c7fba6c4 100644
>>>> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
>>>> @@ -99,6 +99,8 @@ struct panfrost_device {
>>>>  		unsigned long cur_volt;
>>>>  		struct panfrost_devfreq_slot slot[NUM_JOB_SLOTS];
>>>>  	} devfreq;
>>>> +
>>>> +	bool is_resetting;
>>>>  };
>>>>  
>>>>  struct panfrost_mmu {
>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
>>>> index 05c85f45a0de..1b2019e08b43 100644
>>>> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
>>>> @@ -388,13 +388,21 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
>>>>  
>>>>  	mutex_lock(&pfdev->reset_lock);
>>>>  
>>>> +	if (pfdev->is_resetting) {
>>>> +		mutex_unlock(&pfdev->reset_lock);
>>>> +		return;
>>>> +	}
>>>> +	pfdev->is_resetting = true;
>>>> +
>>>> +	mutex_unlock(&pfdev->reset_lock);
>>>> +
>>>>  	for (i = 0; i < NUM_JOB_SLOTS; i++)
>>>>  		drm_sched_stop(&pfdev->js->queue[i].sched, sched_job);
>>>>  
>>>>  	if (sched_job)
>>>>  		drm_sched_increase_karma(sched_job);
>>>>  
>>>> -	/* panfrost_core_dump(pfdev); */
>>>> +	mutex_lock(&pfdev->reset_lock);
>>>>  
>>>>  	panfrost_devfreq_record_transition(pfdev, js);
>>>>  	panfrost_device_reset(pfdev);
>>>> @@ -406,6 +414,7 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
>>>>  	for (i = 0; i < NUM_JOB_SLOTS; i++)
>>>>  		drm_sched_start(&pfdev->js->queue[i].sched, true);
>>>>  
>>>> +	pfdev->is_resetting = false;
>>>>  	mutex_unlock(&pfdev->reset_lock);
>>>>  }
>>>>  
>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>>>> index 148468447ba9..bc6d1862ec8a 100644
>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>> @@ -415,7 +415,10 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
>>>>  	 * this TDR finished and before the newly restarted jobs had a
>>>>  	 * chance to complete.
>>>>  	 */
>>>> -	cancel_delayed_work(&sched->work_tdr);
>>>> +	if (bad->sched != sched)
>>>> +		cancel_delayed_work_sync(&sched->work_tdr);
>>>> +	else
>>>> +		cancel_delayed_work(&sched->work_tdr);
>>>>  }
>>>>  
>>>>  EXPORT_SYMBOL(drm_sched_stop);
>>>>
>>>
>>
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