[PATCHv10 21/26] v4l: vb2-dma-contig: add reference counting for a device from allocator context

Tomasz Stanislawski t.stanislaws at samsung.com
Wed Oct 10 07:46:40 PDT 2012

This patch adds taking reference to the device for MMAP buffers.

Such buffers, may be exported using DMABUF mechanism. If the driver that
created a queue is unloaded then the queue is released, the device might be
released too.  However, buffers cannot be released if they are referenced by
DMABUF descriptor(s). The device pointer kept in a buffer must be valid for the
whole buffer's lifetime. Therefore MMAP buffers should take a reference to the
device to avoid risk of dangling pointers.

Signed-off-by: Tomasz Stanislawski <t.stanislaws at samsung.com>
Acked-by: Hans Verkuil <hans.verkuil at cisco.com>
 drivers/media/v4l2-core/videobuf2-dma-contig.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
index b138b5c..2d661fd 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
@@ -148,6 +148,7 @@ static void vb2_dc_put(void *buf_priv)
 	dma_free_coherent(buf->dev, buf->size, buf->vaddr, buf->dma_addr);
+	put_device(buf->dev);
@@ -168,6 +169,9 @@ static void *vb2_dc_alloc(void *alloc_ctx, unsigned long size)
 		return ERR_PTR(-ENOMEM);
+	/* prevent the device from release while the buffer is exported */
+	get_device(dev);
 	buf->dev = dev;
 	buf->size = size;

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