On 21/05/2020 08:00, dinghao.liu@xxxxxxxxxx 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@xxxxxxxxxx>
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++)
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