linux-kernel - Re: [PATCH v3] drm/sched: Add warning for removing hack in drm_sched

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Message-ID: <ebc028f2-3d2d-4f42-a667-df7d6c2b7eb0@damsy.net>
Date: Fri, 31 Oct 2025 15:10:43 +0100
From: Pierre-Eric Pelloux-Prayer <pierre-eric@...sy.net>
To: Philipp Stanner <phasta@...nel.org>,
 Matthew Brost <matthew.brost@...el.com>, Danilo Krummrich <dakr@...nel.org>,
 Christian König <ckoenig.leichtzumerken@...il.com>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org
Subject: Re: [PATCH v3] drm/sched: Add warning for removing hack in
 drm_sched_fini()

Hi Philipp,

Le 23/10/2025 à 14:34, Philipp Stanner a écrit :
> The assembled developers agreed at the X.Org Developers Conference 2025
> that the hack added for amdgpu in drm_sched_fini() shall be removed. It
> shouldn't be needed by amdgpu anymore.
> 
> As it's unclear whether all drivers really follow the life time rule of
> entities having to be torn down before their scheduler, it is reasonable
> to warn for a while before removing the hack.
> 
> Add a warning in drm_sched_fini() that fires if an entity is still
> active.
> 
> Signed-off-by: Philipp Stanner <phasta@...nel.org>
> ---
> Changes in v3:
>    - Add a READ_ONCE() + comment to make the warning slightly less
>      horrible.
> 
> Changes in v2:
>    - Fix broken brackets.
> ---
>   drivers/gpu/drm/scheduler/sched_main.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index 46119aacb809..31039b08c7b9 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -1419,7 +1419,7 @@ void drm_sched_fini(struct drm_gpu_scheduler *sched)
>   		struct drm_sched_rq *rq = sched->sched_rq[i];
>   
>   		spin_lock(&rq->lock);
> -		list_for_each_entry(s_entity, &rq->entities, list)
> +		list_for_each_entry(s_entity, &rq->entities, list) {
>   			/*
>   			 * Prevents reinsertion and marks job_queue as idle,
>   			 * it will be removed from the rq in drm_sched_entity_fini()
> @@ -1440,8 +1440,15 @@ void drm_sched_fini(struct drm_gpu_scheduler *sched)
>   			 * For now, this remains a potential race in all
>   			 * drivers that keep entities alive for longer than
>   			 * the scheduler.
> +			 *
> +			 * The READ_ONCE() is there to make the lockless read
> +			 * (warning about the lockless write below) slightly
> +			 * less broken...
>   			 */
> +			if (!READ_ONCE(s_entity->stopped))
> +				dev_warn(sched->dev, "Tearing down scheduler with active entities!\n");
>   			s_entity->stopped = true;
> +		}

The patch is Acked-by: Pierre-Eric Pelloux-Prayer 
<pierre-eric.pelloux-prayer@....com>

Thanks.


>   		spin_unlock(&rq->lock);
>   		kfree(sched->sched_rq[i]);
>   	}