Re: [PATCH 01/10] drm/amdgpu: introduce amdgpu_lookup_queue_by_doorbell

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

On 8/28/26 11:53, Zhu Lingshan wrote:
> This commit introduces a new helper
> amdgpu_lookup_queue_by_doorbell which helps
> look up a user queue with the given doorbell id
> in a xarray.
> 
> This function takes a kref of the user space queue.

Well absolutely clear NAK to the whole approach.

This is the nonsense Sunil and I have worked quite hard to remove and we certainly shouldn't repeat such mistakes.

When the userq needs to be used from interrupt context we need to hold the xa_lock_irqsave() or otherwise we don't have any guarantee that the userq, userq_mgr or associated fpriv went out of scope.

Grabbing references from this side would obviously result in circle dependencies.

Regards,
Christian.

> 
> Signed-off-by: Zhu Lingshan <lingshan.zhu@amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c | 30 +++++++++++++++++++++++
>  drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h |  2 ++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> index 0a816b3c5ff9..e0639f844a8e 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c
> @@ -609,6 +609,36 @@ struct amdgpu_usermode_queue *amdgpu_userq_get(struct amdgpu_userq_mgr *uq_mgr,
>  	return queue;
>  }
>  
> +/**
> + * amdgpu_lookup_queue_by_doorbell - look up a user queue by doorbell
> + * @xa: user queue XArray indexed by doorbell
> + * @doorbell: doorbell index
> + *
> + * Return: A queue with the doorbell indexed, or NULL if no such a queue found.
> + *
> + * This function increases kref of the queue, the caller
> + * must release the reference with amdgpu_userq_put().
> + */
> +struct amdgpu_usermode_queue *
> +amdgpu_lookup_queue_by_doorbell(struct xarray *xa, u32 doorbell)
> +{
> +	struct amdgpu_usermode_queue *queue;
> +	unsigned long flags;
> +
> +	xa_lock_irqsave(xa, flags);
> +	queue = xa_load(xa, doorbell);
> +	if (!queue)
> +		goto out_unlock;
> +
> +	if (!kref_get_unless_zero(&queue->refcount))
> +		queue = NULL;
> +
> +out_unlock:
> +	xa_unlock_irqrestore(xa, flags);
> +
> +	return queue;
> +}
> +
>  void amdgpu_userq_put(struct amdgpu_usermode_queue *queue)
>  {
>  	if (queue)
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
> index 6412a7f7b6ef..8fc73862f64e 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_userq.h
> @@ -151,6 +151,8 @@ struct amdgpu_db_info {
>  };
>  
>  struct amdgpu_usermode_queue *amdgpu_userq_get(struct amdgpu_userq_mgr *uq_mgr, u32 qid);
> +struct amdgpu_usermode_queue *
> +amdgpu_lookup_queue_by_doorbell(struct xarray *xa, u32 doorbell);
>  void amdgpu_userq_put(struct amdgpu_usermode_queue *queue);
>  
>  int amdgpu_userq_ioctl(struct drm_device *dev, void *data, struct drm_file *filp);