linux-kernel - Re: [PATCH] drm/sched: Don't crash kernel on wrong params

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Message-ID: <c4a10ad7-22c0-412c-a456-d2dd0f049ac9@ursulin.net>
Date: Fri, 7 Nov 2025 14:42:21 +0000
From: Tvrtko Ursulin <tursulin@...ulin.net>
To: Philipp Stanner <phasta@...nel.org>,
 Matthew Brost <matthew.brost@...el.com>, Danilo Krummrich <dakr@...nel.org>,
 Christian König <ckoenig.leichtzumerken@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/sched: Don't crash kernel on wrong params


On 07/11/2025 12:55, Philipp Stanner wrote:
> drm_sched_job_arm() just panics the kernel with BUG_ON() in case of an
> entity being NULL. While drm_sched_job_arm() crashing or not effectively
> arming jobs is certainly a huge issue that needs to be noticed,
> completely shooting down the kernel reduces the probability of reaching
> and debugging a system to 0.
> 
> Moreover, the checkpatch script by now strongly discourages all new uses
> of BUG_ON() for this reason.
> 
> Replace the BUG_ON() in drm_sched_job_arm() with a WARN_ON().
> 
> Signed-off-by: Philipp Stanner <phasta@...nel.org>
> ---
>   drivers/gpu/drm/scheduler/sched_main.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index 1d4f1b822e7b..3bf4ae0ca4bc 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -857,7 +857,7 @@ void drm_sched_job_arm(struct drm_sched_job *job)
>   	struct drm_gpu_scheduler *sched;
>   	struct drm_sched_entity *entity = job->entity;
>   
> -	BUG_ON(!entity);
> +	WARN_ON(!entity);
>   	drm_sched_entity_select_rq(entity);

void drm_sched_entity_select_rq(struct drm_sched_entity *entity)
{
	struct dma_fence *fence;
	struct drm_gpu_scheduler *sched;
	struct drm_sched_rq *rq;

	/* single possible engine and already selected */
	if (!entity->sched_list)

Still the same end result.

I believe best practice is to simply not have BUG_ON's followed by null 
pointer dereferences since they add no value. Ie. it should just be 
removed and not replaced.

Regards,

Tvrtko

Regards,

Tvrtko

>   	sched = entity->rq->sched;
>