Merge tag 'tag-for-linus-3.9' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf

Pull dma-buf framework updates from Sumit Semwal:
 "Refcounting implemented for vmap in core dma-buf"

* tag 'tag-for-linus-3.9' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf:
  CHROMIUM: dma-buf: restore args on failure of dma_buf_mmap
  dma-buf: implement vmap refcounting in the interface logic

1 files changed, 5 insertions, 1 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