See the comments in the code. Basically if the seqno is already
signalled then we get a NULL fence. If we then put the NULL fence
in a binary syncobj it counts as unsignalled, making that syncobj
pretty much useless for all expected uses.
Not 100% sure about the transfer to a timeline syncobj but I
believe it is needed there too, as AFAICT the add_point function
assumes the fence isn't NULL.
Fixes: ea569910cbab ("drm/syncobj: add transition iotcls between binary and timeline v2")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Bas Nieuwenhuizen <bas@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_syncobj.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index fdd2ec87cdd1..eb28a40400d2 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -861,6 +861,19 @@ static int drm_syncobj_transfer_to_timeline(struct drm_file *file_private,
&fence);
if (ret)
goto err;
+
+ /* If the requested seqno is already signaled drm_syncobj_find_fence may
+ * return a NULL fence. To make sure the recipient gets signalled, use
+ * a new fence instead.
+ */
+ if (!fence) {
+ fence = dma_fence_allocate_private_stub();
+ if (!fence) {
+ ret = -ENOMEM;
+ goto err;
+ }
+ }
+
chain = kzalloc(sizeof(struct dma_fence_chain), GFP_KERNEL);
if (!chain) {
ret = -ENOMEM;
@@ -890,6 +903,19 @@ drm_syncobj_transfer_to_binary(struct drm_file *file_private,
args->src_point, args->flags, &fence);
if (ret)
goto err;
+
+ /* If the requested seqno is already signaled drm_syncobj_find_fence may
+ * return a NULL fence. To make sure the recipient gets signalled, use
+ * a new fence instead.
+ */
+ if (!fence) {
+ fence = dma_fence_allocate_private_stub();
+ if (!fence) {
+ ret = -ENOMEM;
+ goto err;
+ }
+ }
+
drm_syncobj_replace_fence(binary_syncobj, fence);
dma_fence_put(fence);
err:
--
2.34.1
