dma-buf: fix racing conflict of dma_heap_add()

Racing conflict could be:
task A                 task B
list_for_each_entry
strcmp(h->name))
                       list_for_each_entry
                       strcmp(h->name)
kzalloc                kzalloc
......                 .....
device_create          device_create
list_add
                       list_add

The root cause is that task B has no idea about the fact someone
else(A) has inserted heap with same name when it calls list_add,
so a potential collision occurs.

Fixes: c02a81fb ("dma-buf: Add dma-buf heaps framework")
Signed-off-by: Dawei Li <set_pte_at@outlook.com>
Acked-by: Andrew Davis <afd@ti.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/TYCP286MB2323873BBDF88020781FB986CA3B9@TYCP286MB2323.JPNP286.PROD.OUTLOOK.COM

drivers/dma-buf/dma-heap.c

@@ -233,18 +233,6 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
 		return ERR_PTR(-EINVAL);
 	}
 
-	/* check the name is unique */
-	mutex_lock(&heap_list_lock);
-	list_for_each_entry(h, &heap_list, list) {
-		if (!strcmp(h->name, exp_info->name)) {
-			mutex_unlock(&heap_list_lock);
-			pr_err("dma_heap: Already registered heap named %s\n",
-			       exp_info->name);
-			return ERR_PTR(-EINVAL);
-		}
-	}
-	mutex_unlock(&heap_list_lock);
-
 	heap = kzalloc(sizeof(*heap), GFP_KERNEL);
 	if (!heap)
 		return ERR_PTR(-ENOMEM);
@@ -283,13 +271,27 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
 		err_ret = ERR_CAST(dev_ret);
 		goto err2;
 	}
-	/* Add heap to the list */
+
 	mutex_lock(&heap_list_lock);
+	/* check the name is unique */
+	list_for_each_entry(h, &heap_list, list) {
+		if (!strcmp(h->name, exp_info->name)) {
+			mutex_unlock(&heap_list_lock);
+			pr_err("dma_heap: Already registered heap named %s\n",
+			       exp_info->name);
+			err_ret = ERR_PTR(-EINVAL);
+			goto err3;
+		}
+	}
+
+	/* Add heap to the list */
 	list_add(&heap->list, &heap_list);
 	mutex_unlock(&heap_list_lock);
 
 	return heap;
 
+err3:
+	device_destroy(dma_heap_class, heap->heap_devt);
 err2:
 	cdev_del(&heap->heap_cdev);
 err1: