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

[John Stultz]

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

Cc: Sumit Semwal <sumit.sem...@linaro.org>
Cc: Andrew F. Davis <a...@ti.com>
Cc: Benjamin Gaignard <benjamin.gaign...@linaro.org>
Cc: Liam Mark <lm...@codeaurora.org>
Cc: Laura Abbott <labb...@kernel.org>
Cc: Brian Starkey <brian.star...@arm.com>
Cc: linux-me...@vger.kernel.org
Cc: dri-de...@lists.freedesktop.org
Signed-off-by: John Stultz <john.stu...@linaro.org>
---
 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