[PATCH] drm/display/dp_mst: Fix missing check for return value of drm_atomic_get_mst_payload_state()

[Chenyuan Mi]

The drm_atomic_get_mst_payload_state() function may
return NULL, which may cause null pointer deference,
and most other callsites of drm_atomic_get_mst_payload_state()
do Null check. Add Null check for return value of
drm_atomic_get_mst_payload_state().

Found by our static analysis tool.

Signed-off-by: Chenyuan Mi <cym...@fudan.edu.cn>
---
 drivers/gpu/drm/display/drm_dp_mst_topology.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c 
b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 38dab76ae69e..27f4bcf409ea 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -4434,6 +4434,8 @@ void drm_dp_mst_atomic_wait_for_dependencies(struct 
drm_atomic_state *state)
 
                        new_payload = 
drm_atomic_get_mst_payload_state(new_mst_state,
                                                                       
old_payload->port);
+                       if (!new_payload)
+                               continue;
                        new_payload->vc_start_slot = old_payload->vc_start_slot;
                }
        }
-- 
2.17.1