Messages in this thread | | | Subject | Re: [PATCH] drm/panfrost: fix runtime pm imbalance on error | From | Steven Price <> | Date | Fri, 22 May 2020 14:09:24 +0100 |
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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++)
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