drm/syncobj: handle NULL fence in syncobj_eventfd_entry_func

From Erik Kurzinger
20e1e1a2b8a4525301a76bd9afb856a7606a3a34 in linux-6.6.y/6.6.19
2aa6f5b0fd052e363bb9d4b547189f0bf6b3d6d3 in mainline linux

diff --git a/sys/dev/pci/drm/drm_syncobj.c b/sys/dev/pci/drm/drm_syncobj.c
index 9d722d5..841bc90 100644 (file)
--- a/sys/dev/pci/drm/drm_syncobj.c
+++ b/sys/dev/pci/drm/drm_syncobj.c
@@ -1446,10 +1446,21 @@ syncobj_eventfd_entry_func(struct drm_syncobj *syncobj,
 
        /* This happens inside the syncobj lock */
        fence = dma_fence_get(rcu_dereference_protected(syncobj->fence, 1));
+       if (!fence)
+               return;
+
        ret = dma_fence_chain_find_seqno(&fence, entry->point);
-       if (ret != 0 || !fence) {
+       if (ret != 0) {
+               /* The given seqno has not been submitted yet. */
                dma_fence_put(fence);
                return;
+       } else if (!fence) {
+               /* If dma_fence_chain_find_seqno returns 0 but sets the fence
+                * to NULL, it implies that the given seqno is signaled and a
+                * later seqno has already been submitted. Assign a stub fence
+                * so that the eventfd still gets signaled below.
+                */
+               fence = dma_fence_get_stub();
        }
 
        list_del_init(&entry->node);