dma-buf: add ref counting for module as exporter
Add reference counting on a kernel module that exports dma-buf and
implements its operations. This prevents the module from being unloaded
while DMABUF file is in use.
The original patch [1] was submitted by Tomasz Stanislawski, but this
is a simpler way to do it.
v3: call module_put() as late as possible, per gregkh's comment.
v2: move owner to struct dma_buf, and use DEFINE_DMA_BUF_EXPORT_INFO
macro to simplify the change.
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
[1]: https://lkml.org/lkml/2012/8/8/163
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 2f0b431..f98bd70 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -115,6 +115,8 @@
* @attachments: list of dma_buf_attachment that denotes all devices attached.
* @ops: dma_buf_ops associated with this buffer object.
* @exp_name: name of the exporter; useful for debugging.
+ * @owner: pointer to exporter module; used for refcounting when exporter is a
+ * kernel module.
* @list_node: node for dma_buf accounting and debugging.
* @priv: exporter specific private data for this buffer object.
* @resv: reservation object linked to this dma-buf
@@ -129,6 +131,7 @@
unsigned vmapping_counter;
void *vmap_ptr;
const char *exp_name;
+ struct module *owner;
struct list_head list_node;
void *priv;
struct reservation_object *resv;
@@ -164,7 +167,8 @@
/**
* struct dma_buf_export_info - holds information needed to export a dma_buf
- * @exp_name: name of the exporting module - useful for debugging.
+ * @exp_name: name of the exporter - useful for debugging.
+ * @owner: pointer to exporter module - used for refcounting kernel module
* @ops: Attach allocator-defined dma buf ops to the new buffer
* @size: Size of the buffer
* @flags: mode flags for the file
@@ -176,6 +180,7 @@
*/
struct dma_buf_export_info {
const char *exp_name;
+ struct module *owner;
const struct dma_buf_ops *ops;
size_t size;
int flags;
@@ -187,7 +192,8 @@
* helper macro for exporters; zeros and fills in most common values
*/
#define DEFINE_DMA_BUF_EXPORT_INFO(a) \
- struct dma_buf_export_info a = { .exp_name = KBUILD_MODNAME }
+ struct dma_buf_export_info a = { .exp_name = KBUILD_MODNAME, \
+ .owner = THIS_MODULE }
/**
* get_dma_buf - convenience wrapper for get_file.