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-rw-r--r--Documentation/dma-buf-sharing.txt6
-rw-r--r--drivers/base/dma-buf.c43
-rw-r--r--include/linux/dma-buf.h4
3 files changed, 46 insertions, 7 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index 0188903bc9e1..4966b1be42ac 100644
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -302,7 +302,11 @@ Access to a dma_buf from the kernel context involves three steps:
void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
The vmap call can fail if there is no vmap support in the exporter, or if it
- runs out of vmalloc space. Fallback to kmap should be implemented.
+ runs out of vmalloc space. Fallback to kmap should be implemented. Note that
+ the dma-buf layer keeps a reference count for all vmap access and calls down
+ into the exporter's vmap function only when no vmapping exists, and only
+ unmaps it once. Protection against concurrent vmap/vunmap calls is provided
+ by taking the dma_buf->lock mutex.
3. Finish access
diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
index ff5b745c4705..394523807a6d 100644
--- a/drivers/base/dma-buf.c
+++ b/drivers/base/dma-buf.c
@@ -39,6 +39,8 @@ static int dma_buf_release(struct inode *inode, struct file *file)
dmabuf = file->private_data;
+ BUG_ON(dmabuf->vmapping_counter);
+
dmabuf->ops->release(dmabuf);
kfree(dmabuf);
return 0;
@@ -481,12 +483,34 @@ EXPORT_SYMBOL_GPL(dma_buf_mmap);
*/
void *dma_buf_vmap(struct dma_buf *dmabuf)
{
+ void *ptr;
+
if (WARN_ON(!dmabuf))
return NULL;
- if (dmabuf->ops->vmap)
- return dmabuf->ops->vmap(dmabuf);
- return NULL;
+ if (!dmabuf->ops->vmap)
+ return NULL;
+
+ mutex_lock(&dmabuf->lock);
+ if (dmabuf->vmapping_counter) {
+ dmabuf->vmapping_counter++;
+ BUG_ON(!dmabuf->vmap_ptr);
+ ptr = dmabuf->vmap_ptr;
+ goto out_unlock;
+ }
+
+ BUG_ON(dmabuf->vmap_ptr);
+
+ ptr = dmabuf->ops->vmap(dmabuf);
+ if (IS_ERR_OR_NULL(ptr))
+ goto out_unlock;
+
+ dmabuf->vmap_ptr = ptr;
+ dmabuf->vmapping_counter = 1;
+
+out_unlock:
+ mutex_unlock(&dmabuf->lock);
+ return ptr;
}
EXPORT_SYMBOL_GPL(dma_buf_vmap);
@@ -500,7 +524,16 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
if (WARN_ON(!dmabuf))
return;
- if (dmabuf->ops->vunmap)
- dmabuf->ops->vunmap(dmabuf, vaddr);
+ BUG_ON(!dmabuf->vmap_ptr);
+ BUG_ON(dmabuf->vmapping_counter == 0);
+ BUG_ON(dmabuf->vmap_ptr != vaddr);
+
+ mutex_lock(&dmabuf->lock);
+ if (--dmabuf->vmapping_counter == 0) {
+ if (dmabuf->ops->vunmap)
+ dmabuf->ops->vunmap(dmabuf, vaddr);
+ dmabuf->vmap_ptr = NULL;
+ }
+ mutex_unlock(&dmabuf->lock);
}
EXPORT_SYMBOL_GPL(dma_buf_vunmap);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 3d754a394e92..9978b614a1aa 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -119,8 +119,10 @@ struct dma_buf {
struct file *file;
struct list_head attachments;
const struct dma_buf_ops *ops;
- /* mutex to serialize list manipulation and attach/detach */
+ /* mutex to serialize list manipulation, attach/detach and vmap/unmap */
struct mutex lock;
+ unsigned vmapping_counter;
+ void *vmap_ptr;
void *priv;
};