[v3] drm/sched: Add warning for removing hack in drm_sched_fini()

[PATCH v3] drm/sched: Add warning for removing hack in drm_sched_fini()

Posted by Philipp Stanner 3 months, 2 weeks ago

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@kernel.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;
+		}
 		spin_unlock(&rq->lock);
 		kfree(sched->sched_rq[i]);
 	}
-- 
2.49.0

Re: [PATCH v3] drm/sched: Add warning for removing hack in drm_sched_fini()

Posted by Pierre-Eric Pelloux-Prayer 3 months, 1 week ago

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@kernel.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@amd.com>

Thanks.


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

Re: [PATCH v3] drm/sched: Add warning for removing hack in drm_sched_fini()

Posted by Philipp Stanner 3 months, 1 week ago

On Fri, 2025-10-31 at 15:10 +0100, Pierre-Eric Pelloux-Prayer wrote:
> 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@kernel.org>

[…]

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

Pushed to drm-misc-next, thanks.

For the future: b4 / maintainer-tools wasn't able to automatically
harvest your Acked-by. Would be helpful if you have the A-b on a single
line without line break and without other content in the future

Have a nice weekend,
P.

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

Re: [PATCH v3] drm/sched: Add warning for removing hack in drm_sched_fini()

Posted by Philipp Stanner 3 months, 1 week ago

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@kernel.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]);
>  	}