[PATCH 4/6] dma-buf: lock the reservation object during (un)map_dma_buf v3

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

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
v3: rebased on sgt caching

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/dma-buf/dma-buf.c | 15 ++++++---------
 include/linux/dma-buf.h   |  6 ++++++
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index e68322c953a9..21608306349d 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -686,10 +686,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
 	if (WARN_ON(!attach || !attach->dmabuf))
 		return ERR_PTR(-EINVAL);
 
-	if (attach->sgt)
-		return attach->sgt;
-
-	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);
 
@@ -742,11 +741,9 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
 	if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
 		return;
 
-	if (attach->sgt == 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 a40f8f586a95..e964077a7e7e 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -128,6 +128,9 @@ struct dma_buf_ops {
 	 * any other kind of sharing that the exporter might wish to make
 	 * available to buffer-users.
 	 *
+	 * This is always called with the dmabuf->resv object locked when
+	 * no_sgt_cache is true.
+	 *
 	 * Returns:
 	 *
 	 * A &sg_table scatter list of or the backing storage of the DMA buffer,
@@ -148,6 +151,9 @@ 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 always called with the dmabuf->resv object locked when
+	 * no_sgt_cache is true.
 	 */
 	void (*unmap_dma_buf)(struct dma_buf_attachment *,
 			      struct sg_table *,
-- 
2.14.1

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