@@ -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
@@ -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;
@@ -482,12 +484,34 @@ 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);
@@ -501,7 +525,15 @@ 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);
+
+ 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);
@@ -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;
};
All drivers which implement this need to have some sort of refcount to allow concurrent vmap usage. Hence implement this in the dma-buf core. To protect against concurrent calls we need a lock, which potentially causes new funny locking inversions. But this shouldn't be a problem for exporters with statically allocated backing storage, and more dynamic drivers have decent issues already anyway. Inspired by some refactoring patches from Aaron Plattner, who implemented the same idea, but only for drm/prime drivers. v2: Check in dma_buf_release that no dangling vmaps are left. Suggested by Aaron Plattner. We might want to do similar checks for attachments, but that's for another patch. Also fix up ERR_PTR return for vmap. Cc: Aaron Plattner <aplattner@nvidia.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> --- Compile-tested only - Aaron has been bugging me too a bit too often about this on irc. Cheers, Daniel --- Documentation/dma-buf-sharing.txt | 6 +++++- drivers/base/dma-buf.c | 42 ++++++++++++++++++++++++++++++++++----- include/linux/dma-buf.h | 4 +++- 3 files changed, 45 insertions(+), 7 deletions(-)