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

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Message-ID: <81430487-0aa0-8c93-653f-d7a608f3dbff@baylibre.com>
Date:   Mon, 7 Oct 2019 15:09:01 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Steven Price <steven.price@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:     Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panfrost: Handle resetting on timeout better

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@....com>
> ---
> 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 !

>  
>  	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