Re: [PATCH] drm/panfrost: Handle resetting on timeout better

[Tomeu Vizoso]

On 10/7/19 6:09 AM, Neil Armstrong wrote:
> Hi Steven,
>
> On 07/10/2019 14:50, Steven Price wrote:
> > 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.
> >
> > When stopping other slots use cancel_delayed_work_sync() to ensure that
> > any timeout started for that slot has completed. Also use
> > mutex_trylock() to obtain reset_lock. This means that only one thread
> > attempts the reset, the other threads will simply complete without doing
> > anything (the first thread will wait for this in the call to
> > cancel_delayed_work_sync()).
> >
> > While we're here and since the function is already dependent on
> > sched_job not being NULL, let's remove the unnecessary checks, along
> > with a commented out call to panfrost_core_dump() which has never
> > existed in mainline.
>
> A Fixes: tags would be welcome here so it would be backported to v5.3
>
> > Signed-off-by: Steven Price <steven.price@xxxxxxx>
> > ---
> > This is a tidied up version of the patch orginally posted here:
> > http://lkml.kernel.org/r/26ae2a4d-8df1-e8db-3060-41638ed63e2a%40arm.com
> >
> >   drivers/gpu/drm/panfrost/panfrost_job.c | 17 +++++++++++------
> >   1 file changed, 11 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> > index a58551668d9a..dcc9a7603685 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> > @@ -381,13 +381,19 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
> >   		job_read(pfdev, JS_TAIL_LO(js)),
> >   		sched_job);
> >   
> > -	mutex_lock(&pfdev->reset_lock);
> > +	if (!mutex_trylock(&pfdev->reset_lock))
> > +		return;
> >   
> > -	for (i = 0; i < NUM_JOB_SLOTS; i++)
> > -		drm_sched_stop(&pfdev->js->queue[i].sched, sched_job);
> > +	for (i = 0; i < NUM_JOB_SLOTS; i++) {
> > +		struct drm_gpu_scheduler *sched = &pfdev->js->queue[i].sched;
> > +
> > +		drm_sched_stop(sched, sched_job);
> > +		if (js != i)
> > +			/* Ensure any timeouts on other slots have finished */
> > +			cancel_delayed_work_sync(&sched->work_tdr);
> > +	}
> >   
> > -	if (sched_job)
> > -		drm_sched_increase_karma(sched_job);
> > +	drm_sched_increase_karma(sched_job);
>
> Indeed looks cleaner.
>
> >   
> >   	spin_lock_irqsave(&pfdev->js->job_lock, flags);
> >   	for (i = 0; i < NUM_JOB_SLOTS; i++) {
> > @@ -398,7 +404,6 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
> >   	}
> >   	spin_unlock_irqrestore(&pfdev->js->job_lock, flags);
> >   
> > -	/* panfrost_core_dump(pfdev); */
>
> This should be cleaned in another patch !

Seems to me that this should be some kind of TODO, see 
etnaviv_core_dump() for the kind of things we could be doing.

Maybe we can delete this line and mention this in the TODO file?

Cheers,

Tomeu

> >   
> >   	panfrost_devfreq_record_transition(pfdev, js);
> >   	panfrost_device_reset(pfdev);
>
> Thanks,
> Testing it right now with the last change removed (doesn't apply on v5.3 with it),
> results in a few hours... or minutes !
>
>
> Neil