drm/i915/gem: Free the fence after a fence-chain lookup failure

If dma_fence_chain_find_seqno() reports an error, it does so in its
preamble before it disposes of the input fence. On handling the
error, we need to drop the reference to the fence.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2292


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: dc61199c ("drm/i915: add syncobj timeline support")
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200806161056.17593-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c

@@ -2289,6 +2289,7 @@ add_timeline_fence_array(struct i915_execbuffer *eb,
 
 		if (err && !(user_fence.flags & I915_EXEC_FENCE_SIGNAL)) {
 			DRM_DEBUG("Syncobj handle missing requested point %llu\n", point);
+			dma_fence_put(fence);
 			drm_syncobj_put(syncobj);
 			return err;
 		}