Re: [RFC][PATCH] dma-heap: Add proper kref handling on dma-buf heaps

[daniel]

On Sat, Jul 25, 2020 at 03:26:33AM +0000, John Stultz wrote:
> Add proper refcounting on the dma_heap structure.
> While existing heaps are built-in, we may eventually
> have heaps loaded from modules, and we'll need to be
> able to properly handle the references to the heaps

Uh I kinda want to wait until we cross that bridge ... this entire vendor
heaps thing still sounds very much like vendor trees hacking around
instead of having upstream drivers using upstream infrastructure.
-Daniel

> 
> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> Cc: Andrew F. Davis <afd@xxxxxx>
> Cc: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxx>
> Cc: Liam Mark <lmark@xxxxxxxxxxxxxx>
> Cc: Laura Abbott <labbott@xxxxxxxxxx>
> Cc: Brian Starkey <Brian.Starkey@xxxxxxx>
> Cc: linux-media@xxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
> ---
>  drivers/dma-buf/dma-heap.c | 31 +++++++++++++++++++++++++++----
>  include/linux/dma-heap.h   |  6 ++++++
>  2 files changed, 33 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> index afd22c9dbdcf..90c3720acc1c 100644
> --- a/drivers/dma-buf/dma-heap.c
> +++ b/drivers/dma-buf/dma-heap.c
> @@ -40,6 +40,8 @@ struct dma_heap {
>  	dev_t heap_devt;
>  	struct list_head list;
>  	struct cdev heap_cdev;
> +	int minor;
> +	struct kref refcount;
>  };
>  
>  static LIST_HEAD(heap_list);
> @@ -190,11 +192,31 @@ void *dma_heap_get_drvdata(struct dma_heap *heap)
>  	return heap->priv;
>  }
>  
> +static void dma_heap_release(struct kref *ref)
> +{
> +	struct dma_heap *heap = container_of(ref, struct dma_heap, refcount);
> +
> +	/* Remove heap from the list */
> +	mutex_lock(&heap_list_lock);
> +	list_del(&heap->list);
> +	mutex_unlock(&heap_list_lock);
> +
> +	device_destroy(dma_heap_class, heap->heap_devt);
> +	cdev_del(&heap->heap_cdev);
> +	xa_erase(&dma_heap_minors, heap->minor);
> +
> +	kfree(heap);
> +}
> +
> +void dma_heap_put(struct dma_heap *h)
> +{
> +	kref_put(&h->refcount, dma_heap_release);
> +}
> +
>  struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>  {
>  	struct dma_heap *heap, *h, *err_ret;
>  	struct device *dev_ret;
> -	unsigned int minor;
>  	int ret;
>  
>  	if (!exp_info->name || !strcmp(exp_info->name, "")) {
> @@ -223,12 +245,13 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>  	if (!heap)
>  		return ERR_PTR(-ENOMEM);
>  
> +	kref_init(&heap->refcount);
>  	heap->name = exp_info->name;
>  	heap->ops = exp_info->ops;
>  	heap->priv = exp_info->priv;
>  
>  	/* Find unused minor number */
> -	ret = xa_alloc(&dma_heap_minors, &minor, heap,
> +	ret = xa_alloc(&dma_heap_minors, &heap->minor, heap,
>  		       XA_LIMIT(0, NUM_HEAP_MINORS - 1), GFP_KERNEL);
>  	if (ret < 0) {
>  		pr_err("dma_heap: Unable to get minor number for heap\n");
> @@ -237,7 +260,7 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>  	}
>  
>  	/* Create device */
> -	heap->heap_devt = MKDEV(MAJOR(dma_heap_devt), minor);
> +	heap->heap_devt = MKDEV(MAJOR(dma_heap_devt), heap->minor);
>  
>  	cdev_init(&heap->heap_cdev, &dma_heap_fops);
>  	ret = cdev_add(&heap->heap_cdev, heap->heap_devt, 1);
> @@ -267,7 +290,7 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>  err2:
>  	cdev_del(&heap->heap_cdev);
>  err1:
> -	xa_erase(&dma_heap_minors, minor);
> +	xa_erase(&dma_heap_minors, heap->minor);
>  err0:
>  	kfree(heap);
>  	return err_ret;
> diff --git a/include/linux/dma-heap.h b/include/linux/dma-heap.h
> index 454e354d1ffb..c1572f29cfac 100644
> --- a/include/linux/dma-heap.h
> +++ b/include/linux/dma-heap.h
> @@ -56,4 +56,10 @@ void *dma_heap_get_drvdata(struct dma_heap *heap);
>   */
>  struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info);
>  
> +/**
> + * dma_heap_put - drops a reference to a dmabuf heaps, potentially freeing it
> + * @heap:		heap pointer
> + */
> +void dma_heap_put(struct dma_heap *heap);
> +
>  #endif /* _DMA_HEAPS_H */
> -- 
> 2.17.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch