Re: [PATCH v1] drm/sched: fix deadlock in drm_sched_entity_kill_jobs_cb

["Christian König" <christian.koenig@amd.com>]

On 10/29/25 10:11, Pierre-Eric Pelloux-Prayer wrote:
> https://gitlab.freedesktop.org/mesa/mesa/-/issues/13908 pointed out
> a possible deadlock:
> 
> [ 1231.611031]  Possible interrupt unsafe locking scenario:
> 
> [ 1231.611033]        CPU0                    CPU1
> [ 1231.611034]        ----                    ----
> [ 1231.611035]   lock(&xa->xa_lock#17);
> [ 1231.611038]                                local_irq_disable();
> [ 1231.611039]                                lock(&fence->lock);
> [ 1231.611041]                                lock(&xa->xa_lock#17);
> [ 1231.611044]   <Interrupt>
> [ 1231.611045]     lock(&fence->lock);
> [ 1231.611047]
>                 *** DEADLOCK ***
> 
> My initial fix was to replace xa_erase by xa_erase_irq, but Christian
> pointed out that calling dma_fence_add_callback from a callback can
> also deadlock if the signalling fence and the one passed to
> dma_fence_add_callback share the same lock.
> 
> To fix both issues, the code iterating on dependencies and re-arming them
> is moved out to drm_sched_entity_kill_jobs_work.
> 
> Suggested-by: Christian König <christian.koenig@amd.com>
> Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>  drivers/gpu/drm/scheduler/sched_entity.c | 34 +++++++++++++-----------
>  1 file changed, 19 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> index c8e949f4a568..fe174a4857be 100644
> --- a/drivers/gpu/drm/scheduler/sched_entity.c
> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> @@ -173,26 +173,15 @@ int drm_sched_entity_error(struct drm_sched_entity *entity)
>  }
>  EXPORT_SYMBOL(drm_sched_entity_error);
>  
> +static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
> +					  struct dma_fence_cb *cb);
> +
>  static void drm_sched_entity_kill_jobs_work(struct work_struct *wrk)
>  {
>  	struct drm_sched_job *job = container_of(wrk, typeof(*job), work);
> -
> -	drm_sched_fence_scheduled(job->s_fence, NULL);
> -	drm_sched_fence_finished(job->s_fence, -ESRCH);
> -	WARN_ON(job->s_fence->parent);
> -	job->sched->ops->free_job(job);
> -}
> -
> -/* Signal the scheduler finished fence when the entity in question is killed. */
> -static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
> -					  struct dma_fence_cb *cb)
> -{
> -	struct drm_sched_job *job = container_of(cb, struct drm_sched_job,
> -						 finish_cb);
> +	struct dma_fence *f;
>  	unsigned long index;
>  
> -	dma_fence_put(f);
> -
>  	/* Wait for all dependencies to avoid data corruptions */
>  	xa_for_each(&job->dependencies, index, f) {
>  		struct drm_sched_fence *s_fence = to_drm_sched_fence(f);
> @@ -220,6 +209,21 @@ static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
>  		dma_fence_put(f);
>  	}
>  
> +	drm_sched_fence_scheduled(job->s_fence, NULL);
> +	drm_sched_fence_finished(job->s_fence, -ESRCH);
> +	WARN_ON(job->s_fence->parent);
> +	job->sched->ops->free_job(job);
> +}
> +
> +/* Signal the scheduler finished fence when the entity in question is killed. */
> +static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
> +					  struct dma_fence_cb *cb)
> +{
> +	struct drm_sched_job *job = container_of(cb, struct drm_sched_job,
> +						 finish_cb);
> +
> +	dma_fence_put(f);
> +
>  	INIT_WORK(&job->work, drm_sched_entity_kill_jobs_work);
>  	schedule_work(&job->work);
>  }