dma_fence_chain_find_seqno only ever returns the top fence in the
chain or an unsignalled fence. Hence if we request a seqno that
is already signalled it returns a NULL fence. Some callers are
not prepared to handle this, like the syncobj transfer functions
for example.
This behavior is "new" with timeline syncobj and it looks like
not all callers were updated. To fix this behavior make sure
that a successful drm_sync_find_fence always returns a non-NULL
fence.
v2: Move the fix to drm_syncobj_find_fence from the transfer
functions.
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 | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index fdd2ec87cdd1..11be91b5709b 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -404,8 +404,17 @@ int drm_syncobj_find_fence(struct drm_file *file_private,
if (*fence) {
ret = dma_fence_chain_find_seqno(fence, point);
- if (!ret)
+ if (!ret) {
+ /* 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_get_stub();
+
goto out;
+ }
dma_fence_put(*fence);
} else {
ret = -EINVAL;
--
2.34.1
