[PATCH] drm/panfrost: fix runtime pm imbalance on error

[PATCH] drm/panfrost: fix runtime pm imbalance on error

[Dinghao Liu]

pm_runtime_get_sync() increments the runtime PM usage counter even
the call returns an error code. Thus a pairing decrement is needed
on the error handling path to keep the counter balanced.

Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
---
 drivers/gpu/drm/panfrost/panfrost_job.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
index 7914b1570841..5719e356c969 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -146,8 +146,10 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
 	int ret;
 
 	ret = pm_runtime_get_sync(pfdev->dev);
-	if (ret < 0)
+	if (ret < 0) {
+		pm_runtime_put_sync_autosuspend(pfdev->dev);
 		return;
+	}
 
 	if (WARN_ON(job_read(pfdev, JS_COMMAND_NEXT(js)))) {
 		pm_runtime_put_sync_autosuspend(pfdev->dev);
-- 
2.17.1

Re: [PATCH] drm/panfrost: fix runtime pm imbalance on error

[Steven Price]

On 20/05/2020 12:05, Dinghao Liu wrote:
> pm_runtime_get_sync() increments the runtime PM usage counter even
> the call returns an error code. Thus a pairing decrement is needed
> on the error handling path to keep the counter balanced.
> 
> Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>

Actually I think we have the opposite problem. To be honest we don't 
handle this situation very well. By the time panfrost_job_hw_submit() is 
called the job has already been added to the pfdev->jobs array, so it's 
considered submitted even if it never actually lands on the hardware. So 
in the case of this function bailing out early we will then (eventually) 
hit a timeout and trigger a GPU reset.

panfrost_job_timedout() iterates through the pfdev->jobs array and calls 
pm_runtime_put_noidle() for each job it finds. So there's no inbalance 
here that I can see.

Have you actually observed the situation where pm_runtime_get_sync() 
returns a failure?

HOWEVER, it appears that by bailing out early the call to 
panfrost_devfreq_record_busy() is never made, which as far as I can see 
means that there may be an extra call to panfrost_devfreq_record_idle() 
when the jobs have timed out. Which could underflow the counter.

But equally looking at panfrost_job_timedout(), we only call 
panfrost_devfreq_record_idle() *once* even though multiple jobs might be 
processed.

There's a completely untested patch below which in theory should fix that...

Steve

----8<---
diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c 
b/drivers/gpu/drm/panfrost/panfrost_job.c
index 7914b1570841..f9519afca29d 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -145,6 +145,8 @@ static void panfrost_job_hw_submit(struct 
panfrost_job *job, int js)
  	u64 jc_head = job->jc;
  	int ret;

+	panfrost_devfreq_record_busy(pfdev);
+
  	ret = pm_runtime_get_sync(pfdev->dev);
  	if (ret < 0)
  		return;
@@ -155,7 +157,6 @@ static void panfrost_job_hw_submit(struct 
panfrost_job *job, int js)
  	}

  	cfg = panfrost_mmu_as_get(pfdev, &job->file_priv->mmu);
-	panfrost_devfreq_record_busy(pfdev);

  	job_write(pfdev, JS_HEAD_NEXT_LO(js), jc_head & 0xFFFFFFFF);
  	job_write(pfdev, JS_HEAD_NEXT_HI(js), jc_head >> 32);
@@ -410,12 +411,12 @@ static void panfrost_job_timedout(struct 
drm_sched_job *sched_job)
  	for (i = 0; i < NUM_JOB_SLOTS; i++) {
  		if (pfdev->jobs[i]) {
  			pm_runtime_put_noidle(pfdev->dev);
+			panfrost_devfreq_record_idle(pfdev);
  			pfdev->jobs[i] = NULL;
  		}
  	}
  	spin_unlock_irqrestore(&pfdev->js->job_lock, flags);

-	panfrost_devfreq_record_idle(pfdev);
  	panfrost_device_reset(pfdev);

  	for (i = 0; i < NUM_JOB_SLOTS; i++)

Re: Re: [PATCH] drm/panfrost: fix runtime pm imbalance on error

[dinghao.liu]

Hi Steve,

There are two bailing out points in panfrost_job_hw_submit(): one is 
the error path beginning from pm_runtime_get_sync(), the other one is 
the error path beginning from WARN_ON() in the if statement. The pm 
imbalance fixed in this patch is between these two paths. I think the 
caller of panfrost_job_hw_submit() cannot distinguish this imbalance 
outside this function. 

panfrost_job_timedout() calls pm_runtime_put_noidle() for every job it 
finds, but all jobs are added to the pfdev->jobs just before calling
panfrost_job_hw_submit(). Therefore I think the imbalance still exists.
But I'm not very sure if we should add pm_runtime_put on the error path
after pm_runtime_get_sync(), or remove pm_runtime_put one the error path
after WARN_ON(). 

As for the problem about panfrost_devfreq_record_busy(), this may be a 
new bug and requires independent patch to fix it.

Regards,
Dinghao


> On 20/05/2020 12:05, Dinghao Liu wrote:
> > pm_runtime_get_sync() increments the runtime PM usage counter even
> > the call returns an error code. Thus a pairing decrement is needed
> > on the error handling path to keep the counter balanced.
> > 
> > Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
> 
> Actually I think we have the opposite problem. To be honest we don't 
> handle this situation very well. By the time panfrost_job_hw_submit() is 
> called the job has already been added to the pfdev->jobs array, so it's 
> considered submitted even if it never actually lands on the hardware. So 
> in the case of this function bailing out early we will then (eventually) 
> hit a timeout and trigger a GPU reset.
> 
> panfrost_job_timedout() iterates through the pfdev->jobs array and calls 
> pm_runtime_put_noidle() for each job it finds. So there's no inbalance 
> here that I can see.
> 
> Have you actually observed the situation where pm_runtime_get_sync() 
> returns a failure?
> 
> HOWEVER, it appears that by bailing out early the call to 
> panfrost_devfreq_record_busy() is never made, which as far as I can see 
> means that there may be an extra call to panfrost_devfreq_record_idle() 
> when the jobs have timed out. Which could underflow the counter.
> 
> But equally looking at panfrost_job_timedout(), we only call 
> panfrost_devfreq_record_idle() *once* even though multiple jobs might be 
> processed.
> 
> There's a completely untested patch below which in theory should fix that...
> 
> Steve
> 
> ----8<---
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c 
> b/drivers/gpu/drm/panfrost/panfrost_job.c
> index 7914b1570841..f9519afca29d 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -145,6 +145,8 @@ static void panfrost_job_hw_submit(struct 
> panfrost_job *job, int js)
>   	u64 jc_head = job->jc;
>   	int ret;
> 
> +	panfrost_devfreq_record_busy(pfdev);
> +
>   	ret = pm_runtime_get_sync(pfdev->dev);
>   	if (ret < 0)
>   		return;
> @@ -155,7 +157,6 @@ static void panfrost_job_hw_submit(struct 
> panfrost_job *job, int js)
>   	}
> 
>   	cfg = panfrost_mmu_as_get(pfdev, &job->file_priv->mmu);
> -	panfrost_devfreq_record_busy(pfdev);
> 
>   	job_write(pfdev, JS_HEAD_NEXT_LO(js), jc_head & 0xFFFFFFFF);
>   	job_write(pfdev, JS_HEAD_NEXT_HI(js), jc_head >> 32);
> @@ -410,12 +411,12 @@ static void panfrost_job_timedout(struct 
> drm_sched_job *sched_job)
>   	for (i = 0; i < NUM_JOB_SLOTS; i++) {
>   		if (pfdev->jobs[i]) {
>   			pm_runtime_put_noidle(pfdev->dev);
> +			panfrost_devfreq_record_idle(pfdev);
>   			pfdev->jobs[i] = NULL;
>   		}
>   	}
>   	spin_unlock_irqrestore(&pfdev->js->job_lock, flags);
> 
> -	panfrost_devfreq_record_idle(pfdev);
>   	panfrost_device_reset(pfdev);
> 
>   	for (i = 0; i < NUM_JOB_SLOTS; i++)

Re: [PATCH] drm/panfrost: fix runtime pm imbalance on error

[Steven Price]

On 21/05/2020 08:00, dinghao.liu@zju.edu.cn wrote:
> Hi Steve,
> 
> There are two bailing out points in panfrost_job_hw_submit(): one is
> the error path beginning from pm_runtime_get_sync(), the other one is
> the error path beginning from WARN_ON() in the if statement. The pm
> imbalance fixed in this patch is between these two paths. I think the
> caller of panfrost_job_hw_submit() cannot distinguish this imbalance
> outside this function.

My point is the caller expects panfrost_job_hw_submit() to increase the 
PM reference count. Since panfrost_job_hw_submit() cannot return an 
error (it's void return) we cannot signal to the caller that the 
reference hasn't been taken.

> panfrost_job_timedout() calls pm_runtime_put_noidle() for every job it
> finds, but all jobs are added to the pfdev->jobs just before calling
> panfrost_job_hw_submit(). Therefore I think the imbalance still exists.

My point's exactly that - the "jobs are added to pfdev->jobs just before 
calling panfrost_job_hw_submit()". Since we don't have a way for 
panfrost_job_hw_submit() to fail it must unconditionally take any 
references that will then be freed later on.

> But I'm not very sure if we should add pm_runtime_put on the error path
> after pm_runtime_get_sync(), or remove pm_runtime_put one the error path
> after WARN_ON().

The pm_runtime_put after the WARN_ON() is a bug. Sorry this is probably 
what confused you - clearly the WARN_ON() situation is never meant to 
happen in the first place, so hopefully this isn't actually possible.

Feel free to send a patch removing it! ;)

> As for the problem about panfrost_devfreq_record_busy(), this may be a
> new bug and requires independent patch to fix it.

Indeed, I'll post a proper patch for that later - I just spotted it 
while looking at the code.

Thanks,

Steve

> Regards,
> Dinghao
> 
> 
>> On 20/05/2020 12:05, Dinghao Liu wrote:
>>> pm_runtime_get_sync() increments the runtime PM usage counter even
>>> the call returns an error code. Thus a pairing decrement is needed
>>> on the error handling path to keep the counter balanced.
>>>
>>> Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
>>
>> Actually I think we have the opposite problem. To be honest we don't
>> handle this situation very well. By the time panfrost_job_hw_submit() is
>> called the job has already been added to the pfdev->jobs array, so it's
>> considered submitted even if it never actually lands on the hardware. So
>> in the case of this function bailing out early we will then (eventually)
>> hit a timeout and trigger a GPU reset.
>>
>> panfrost_job_timedout() iterates through the pfdev->jobs array and calls
>> pm_runtime_put_noidle() for each job it finds. So there's no inbalance
>> here that I can see.
>>
>> Have you actually observed the situation where pm_runtime_get_sync()
>> returns a failure?
>>
>> HOWEVER, it appears that by bailing out early the call to
>> panfrost_devfreq_record_busy() is never made, which as far as I can see
>> means that there may be an extra call to panfrost_devfreq_record_idle()
>> when the jobs have timed out. Which could underflow the counter.
>>
>> But equally looking at panfrost_job_timedout(), we only call
>> panfrost_devfreq_record_idle() *once* even though multiple jobs might be
>> processed.
>>
>> There's a completely untested patch below which in theory should fix that...
>>
>> Steve
>>
>> ----8<---
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c
>> b/drivers/gpu/drm/panfrost/panfrost_job.c
>> index 7914b1570841..f9519afca29d 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
>> @@ -145,6 +145,8 @@ static void panfrost_job_hw_submit(struct
>> panfrost_job *job, int js)
>>    	u64 jc_head = job->jc;
>>    	int ret;
>>
>> +	panfrost_devfreq_record_busy(pfdev);
>> +
>>    	ret = pm_runtime_get_sync(pfdev->dev);
>>    	if (ret < 0)
>>    		return;
>> @@ -155,7 +157,6 @@ static void panfrost_job_hw_submit(struct
>> panfrost_job *job, int js)
>>    	}
>>
>>    	cfg = panfrost_mmu_as_get(pfdev, &job->file_priv->mmu);
>> -	panfrost_devfreq_record_busy(pfdev);
>>
>>    	job_write(pfdev, JS_HEAD_NEXT_LO(js), jc_head & 0xFFFFFFFF);
>>    	job_write(pfdev, JS_HEAD_NEXT_HI(js), jc_head >> 32);
>> @@ -410,12 +411,12 @@ static void panfrost_job_timedout(struct
>> drm_sched_job *sched_job)
>>    	for (i = 0; i < NUM_JOB_SLOTS; i++) {
>>    		if (pfdev->jobs[i]) {
>>    			pm_runtime_put_noidle(pfdev->dev);
>> +			panfrost_devfreq_record_idle(pfdev);
>>    			pfdev->jobs[i] = NULL;
>>    		}
>>    	}
>>    	spin_unlock_irqrestore(&pfdev->js->job_lock, flags);
>>
>> -	panfrost_devfreq_record_idle(pfdev);
>>    	panfrost_device_reset(pfdev);
>>
>>    	for (i = 0; i < NUM_JOB_SLOTS; i++)

Re: Re: [PATCH] drm/panfrost: fix runtime pm imbalance on error

[dinghao.liu]

Thank you for your further explanation! It's all clear for me and I 
will write a new patch to fix this imbalance.

Regards,
Dinghao
> On 21/05/2020 08:00, dinghao.liu@zju.edu.cn wrote:
> > Hi Steve,
> > 
> > There are two bailing out points in panfrost_job_hw_submit(): one is
> > the error path beginning from pm_runtime_get_sync(), the other one is
> > the error path beginning from WARN_ON() in the if statement. The pm
> > imbalance fixed in this patch is between these two paths. I think the
> > caller of panfrost_job_hw_submit() cannot distinguish this imbalance
> > outside this function.
> 
> My point is the caller expects panfrost_job_hw_submit() to increase the 
> PM reference count. Since panfrost_job_hw_submit() cannot return an 
> error (it's void return) we cannot signal to the caller that the 
> reference hasn't been taken.
> 
> > panfrost_job_timedout() calls pm_runtime_put_noidle() for every job it
> > finds, but all jobs are added to the pfdev->jobs just before calling
> > panfrost_job_hw_submit(). Therefore I think the imbalance still exists.
> 
> My point's exactly that - the "jobs are added to pfdev->jobs just before 
> calling panfrost_job_hw_submit()". Since we don't have a way for 
> panfrost_job_hw_submit() to fail it must unconditionally take any 
> references that will then be freed later on.
> 
> > But I'm not very sure if we should add pm_runtime_put on the error path
> > after pm_runtime_get_sync(), or remove pm_runtime_put one the error path
> > after WARN_ON().
> 
> The pm_runtime_put after the WARN_ON() is a bug. Sorry this is probably 
> what confused you - clearly the WARN_ON() situation is never meant to 
> happen in the first place, so hopefully this isn't actually possible.
> 
> Feel free to send a patch removing it! ;)
> 
> > As for the problem about panfrost_devfreq_record_busy(), this may be a
> > new bug and requires independent patch to fix it.
> 
> Indeed, I'll post a proper patch for that later - I just spotted it 
> while looking at the code.
> 
> Thanks,
> 
> Steve
> 
> > Regards,
> > Dinghao
> > 
> > 
> >> On 20/05/2020 12:05, Dinghao Liu wrote:
> >>> pm_runtime_get_sync() increments the runtime PM usage counter even
> >>> the call returns an error code. Thus a pairing decrement is needed
> >>> on the error handling path to keep the counter balanced.
> >>>
> >>> Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
> >>
> >> Actually I think we have the opposite problem. To be honest we don't
> >> handle this situation very well. By the time panfrost_job_hw_submit() is
> >> called the job has already been added to the pfdev->jobs array, so it's
> >> considered submitted even if it never actually lands on the hardware. So
> >> in the case of this function bailing out early we will then (eventually)
> >> hit a timeout and trigger a GPU reset.
> >>
> >> panfrost_job_timedout() iterates through the pfdev->jobs array and calls
> >> pm_runtime_put_noidle() for each job it finds. So there's no inbalance
> >> here that I can see.
> >>
> >> Have you actually observed the situation where pm_runtime_get_sync()
> >> returns a failure?
> >>
> >> HOWEVER, it appears that by bailing out early the call to
> >> panfrost_devfreq_record_busy() is never made, which as far as I can see
> >> means that there may be an extra call to panfrost_devfreq_record_idle()
> >> when the jobs have timed out. Which could underflow the counter.
> >>
> >> But equally looking at panfrost_job_timedout(), we only call
> >> panfrost_devfreq_record_idle() *once* even though multiple jobs might be
> >> processed.
> >>
> >> There's a completely untested patch below which in theory should fix that...
> >>
> >> Steve
> >>
> >> ----8<---
> >> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c
> >> b/drivers/gpu/drm/panfrost/panfrost_job.c
> >> index 7914b1570841..f9519afca29d 100644
> >> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> >> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> >> @@ -145,6 +145,8 @@ static void panfrost_job_hw_submit(struct
> >> panfrost_job *job, int js)
> >>    	u64 jc_head = job->jc;
> >>    	int ret;
> >>
> >> +	panfrost_devfreq_record_busy(pfdev);
> >> +
> >>    	ret = pm_runtime_get_sync(pfdev->dev);
> >>    	if (ret < 0)
> >>    		return;
> >> @@ -155,7 +157,6 @@ static void panfrost_job_hw_submit(struct
> >> panfrost_job *job, int js)
> >>    	}
> >>
> >>    	cfg = panfrost_mmu_as_get(pfdev, &job->file_priv->mmu);
> >> -	panfrost_devfreq_record_busy(pfdev);
> >>
> >>    	job_write(pfdev, JS_HEAD_NEXT_LO(js), jc_head & 0xFFFFFFFF);
> >>    	job_write(pfdev, JS_HEAD_NEXT_HI(js), jc_head >> 32);
> >> @@ -410,12 +411,12 @@ static void panfrost_job_timedout(struct
> >> drm_sched_job *sched_job)
> >>    	for (i = 0; i < NUM_JOB_SLOTS; i++) {
> >>    		if (pfdev->jobs[i]) {
> >>    			pm_runtime_put_noidle(pfdev->dev);
> >> +			panfrost_devfreq_record_idle(pfdev);
> >>    			pfdev->jobs[i] = NULL;
> >>    		}
> >>    	}
> >>    	spin_unlock_irqrestore(&pfdev->js->job_lock, flags);
> >>
> >> -	panfrost_devfreq_record_idle(pfdev);
> >>    	panfrost_device_reset(pfdev);
> >>
> >>    	for (i = 0; i < NUM_JOB_SLOTS; i++)