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/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index c5a9138a6a8d69508c2a062a48baf359379928ef..63a9914e42b8726dd534501d6f9d2517d641891f 100644 (file)
--- 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>
@@ -72,6 +73,7 @@ static int dma_buf_release(struct inode *inode, struct file *file)
        if (dmabuf->resv == (struct reservation_object *)&dmabuf[1])
                reservation_object_fini(dmabuf->resv);
 
+       module_put(dmabuf->owner);
        kfree(dmabuf);
        return 0;
 }
@@ -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 2f0b431b73e0a7a2c8807a694c8c89a4e4b61a29..f98bd7068d55a3f4ddfdb50dc01d95909ab30f45 100644 (file)
--- 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.