[PATCH 2/4] dma-buf: warn about dma_fence_array container rules

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

It's not allowed to nest another dma_fence container into a dma_fence_array
or otherwise we can run into recursion.

Warn about that when we create a dma_fence_array.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/dma-buf/dma-fence-array.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
index 3e07f961e2f3..4bfbcb885bbc 100644
--- a/drivers/dma-buf/dma-fence-array.c
+++ b/drivers/dma-buf/dma-fence-array.c
@@ -176,6 +176,19 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
 
 	array->base.error = PENDING_ERROR;
 
+	/* dma_fence_array objects should never contain any other fence
+	 * containers or otherwise we run into recursion and potential kernel
+	 * stack overflow on operations on the dma_fence_array.
+	 *
+	 * The correct way of handling this is to flatten out the array by the
+	 * caller instead.
+	 *
+	 * Enforce this here by checking that we don't create a dma_fence_array
+	 * with any container inside.
+	 */
+	while (seqno--)
+		WARN_ON(dma_fence_is_container(fences[seqno]));
+
 	return array;
 }
 EXPORT_SYMBOL(dma_fence_array_create);
-- 
2.25.1