[PATCH] drm/xe: Fix NULL pointer dereference in xe_exec_ioctl

["Tapani Pälli" <tapani.palli@intel.com>]

Helper function xe_sync_needs_wait expects sync->fence when accessing
flags, patch makes sure we call only when sync->fence exists.

Fixes NULL pointer dereference seen with Vulkan workloads:

[  118.410401] RIP: 0010:xe_sync_needs_wait+0x27/0x50 [xe]

Fixes: 4ac9048d0501 ("drm/xe: Wait on in-syncs when swicthing to dma-fence mode")
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
---
 drivers/gpu/drm/xe/xe_exec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_exec.c b/drivers/gpu/drm/xe/xe_exec.c
index 730a5c9c2637..ea368f02cb9f 100644
--- a/drivers/gpu/drm/xe/xe_exec.c
+++ b/drivers/gpu/drm/xe/xe_exec.c
@@ -184,7 +184,8 @@ int xe_exec_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 		if (xe_sync_is_ufence(&syncs[num_syncs]))
 			num_ufence++;
 
-		if (!num_in_sync && xe_sync_needs_wait(&syncs[num_syncs]))
+		if (!num_in_sync && syncs[num_syncs].fence &&
+		    xe_sync_needs_wait(&syncs[num_syncs]))
 			num_in_sync++;
 	}
 
-- 
2.52.0