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

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Message-ID: <015c204472811734b1e2a12d044ac3b13926c617.camel@mailbox.org>
Date: Thu, 30 Oct 2025 16:23:44 +0100
From: Philipp Stanner <phasta@...lbox.org>
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()

On Thu, 2025-10-23 at 14:34 +0200, Philipp Stanner wrote:
> 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>

Can someone review this?

At XDC we agreed on removing the hack, but wanted to add a warning
print first for a few releases, to really catch if there are no users
anymore.

Thx
P.

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