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.
v2: move owner to struct dma_buf, and use DEFINE_DMA_BUF_EXPORT_INFO
macro to simplify the change.
Signed-off-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
[1]: https://lkml.org/lkml/2012/8/8/163
---
drivers/dma-buf/dma-buf.c | 10 +++++++++-
include/linux/dma-buf.h | 10 ++++++++--
2 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index c5a9138a6a8d..0eff4bf56ef6 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -29,6 +29,7 @@
#include <linux/anon_inodes.h>
#include <linux/export.h>
#include <linux/debugfs.h>
+#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/poll.h>
#include <linux/reservation.h>
@@ -64,6 +65,7 @@ static int dma_buf_release(struct inode *inode, struct file *file)
BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active);
dmabuf->ops->release(dmabuf);
+ module_put(dmabuf->owner);
mutex_lock(&db_list.lock);
list_del(&dmabuf->list_node);
@@ -302,14 +304,20 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
return ERR_PTR(-EINVAL);
}
+ if (!try_module_get(exp_info->owner))
+ return ERR_PTR(-ENOENT);
+
dmabuf = kzalloc(alloc_size, GFP_KERNEL);
- if (dmabuf == NULL)
+ if (!dmabuf) {
+ module_put(exp_info->owner);
return ERR_PTR(-ENOMEM);
+ }
dmabuf->priv = exp_info->priv;
dmabuf->ops = exp_info->ops;
dmabuf->size = exp_info->size;
dmabuf->exp_name = exp_info->exp_name;
+ dmabuf->owner = exp_info->owner;
init_waitqueue_head(&dmabuf->poll);
dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 2f0b431b73e0..f98bd7068d55 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -115,6 +115,8 @@ struct dma_buf_ops {
* @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 @@ struct dma_buf {
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_attachment {
/**
* 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_attachment {
*/
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 @@ struct dma_buf_export_info {
* 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.
--
1.9.1
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