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From dd2c03120004f3bfed8b4f6500c33957b1bae807 Mon Sep 17 00:00:00 2001
From: John Stultz <jstultz@google.com>
Date: Mon, 11 Sep 2023 10:30:31 +0800
Subject: [PATCH 1/2] FROMLIST: dma-heap: Add proper kref handling on dma-buf
heaps
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
Also moves minor tracking into the heap structure so
we can properly free things.
[Yong: Just add comment for "minor" and "refcount"]
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Signed-off-by: Vijayanand Jitta <quic_vjitta@quicinc.com>
Signed-off-by: Atul Dhudase <quic_adhudase@quicinc.com>
Upstream-Status: Submitted [https://lore.kernel.org/lkml/20230911023038.30649-3-yong.wu@mediatek.com/]
---
drivers/dma-buf/dma-heap.c | 38 ++++++++++++++++++++++++++++++++++----
include/linux/dma-heap.h | 6 ++++++
2 files changed, 40 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index 84ae708fafe7..59328045975a 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c
@@ -12,6 +12,7 @@
#include <linux/dma-buf.h>
#include <linux/err.h>
#include <linux/xarray.h>
+#include <linux/kref.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/nospec.h>
@@ -31,6 +32,8 @@
* @heap_devt heap device node
* @list list head connecting to list of heaps
* @heap_cdev heap char device
+ * @minor: heap device node minor number
+ * @refcount: reference counter for this heap device
*
* Represents a heap of memory from which buffers can be made.
*/
@@ -41,6 +44,8 @@ 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);
@@ -220,7 +225,6 @@ 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, "")) {
@@ -237,12 +241,13 @@ 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");
@@ -251,7 +256,7 @@ 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);
@@ -295,12 +300,37 @@ 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;
}
+static void dma_heap_release(struct kref *ref)
+{
+ struct dma_heap *heap = container_of(ref, struct dma_heap, refcount);
+
+ /* Note, we already holding the heap_list_lock here */
+ list_del(&heap->list);
+
+ 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)
+{
+ /*
+ * Take the heap_list_lock now to avoid racing with code
+ * scanning the list and then taking a kref.
+ */
+ mutex_lock(&heap_list_lock);
+ kref_put(&h->refcount, dma_heap_release);
+ mutex_unlock(&heap_list_lock);
+}
+
static char *dma_heap_devnode(const struct device *dev, umode_t *mode)
{
return kasprintf(GFP_KERNEL, "dma_heap/%s", dev_name(dev));
diff --git a/include/linux/dma-heap.h b/include/linux/dma-heap.h
index 0c05561cad6e..f8c986dd9a8b 100644
--- a/include/linux/dma-heap.h
+++ b/include/linux/dma-heap.h
@@ -65,4 +65,10 @@ const char *dma_heap_get_name(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 heap, potentially freeing it
+ * @heap: the heap whose reference count to decrement
+ */
+void dma_heap_put(struct dma_heap *heap);
+
#endif /* _DMA_HEAPS_H */
--
2.25.1
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