Re: [PATCH 2/4] dma-buf: lock the reservation object during (un)map_dma_buf v2

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On 06/22/2018 10:11 PM, Christian König wrote:
First step towards unpinned DMA buf operation.

I've checked the DRM drivers to potential locking of the reservation
object, but essentially we need to audit all implementations of the
dma_buf _ops for this to work.

v2: reordered

Signed-off-by: Christian König <christian.koenig@xxxxxxx>

looks good for me.

Reviewed-by: Junwei Zhang <Jerry.Zhang@xxxxxxx>

Jerry
---
  drivers/dma-buf/dma-buf.c | 9 ++++++---
  include/linux/dma-buf.h   | 4 ++++
  2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index dc94e76e2e2a..49f23b791eb8 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -665,7 +665,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
  	if (WARN_ON(!attach || !attach->dmabuf))
  		return ERR_PTR(-EINVAL);

-	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
+	reservation_object_lock(attach->dmabuf->resv, NULL);
+	sg_table = dma_buf_map_attachment_locked(attach, direction);
+	reservation_object_unlock(attach->dmabuf->resv);
  	if (!sg_table)
  		sg_table = ERR_PTR(-ENOMEM);

@@ -715,8 +717,9 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
  	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
  		return;

-	attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
-						direction);
+	reservation_object_lock(attach->dmabuf->resv, NULL);
+	dma_buf_unmap_attachment_locked(attach, sg_table, direction);
+	reservation_object_unlock(attach->dmabuf->resv);
  }
  EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);

diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index a25e754ae2f7..024658d1f22e 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -118,6 +118,8 @@ struct dma_buf_ops {
  	 * any other kind of sharing that the exporter might wish to make
  	 * available to buffer-users.
  	 *
+	 * This is called with the dmabuf->resv object locked.
+	 *
  	 * Returns:
  	 *
  	 * A &sg_table scatter list of or the backing storage of the DMA buffer,
@@ -138,6 +140,8 @@ struct dma_buf_ops {
  	 * It should also unpin the backing storage if this is the last mapping
  	 * of the DMA buffer, it the exporter supports backing storage
  	 * migration.
+	 *
+	 * This is called with the dmabuf->resv object locked.
  	 */
  	void (*unmap_dma_buf)(struct dma_buf_attachment *,
  			      struct sg_table *,

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