dma-buf: warn about dma_fence_array container rules v2

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.

v2: fix comment style and typo in the warning pointed out by Thomas

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220204100429.2049-3-christian.koenig@amd.com

diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
index 3e07f96..cb1bacb 100644 (file)
--- a/drivers/dma-buf/dma-fence-array.c
+++ b/drivers/dma-buf/dma-fence-array.c
@@ -176,6 +176,20 @@ 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 (num_fences--)
+               WARN_ON(dma_fence_is_container(fences[num_fences]));
+
        return array;
 }
 EXPORT_SYMBOL(dma_fence_array_create);