drm/i915: don't leak global_timeline

We need to clean up the global_timeline in i915_gem_load_cleanup.

v2: don't forget about the struct_mutex, and also WARN_ON if we have any
remaining timelines before purging the global_timeline.

v3: it might be a good idea to first remove the global_timeline...duh!

Fixes: 73cb97010d4f ("drm/i915: Combine seqno + tracking into a global timeline struct")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1479415087-13216-1-git-send-email-matthew.auld@intel.com
Link: http://patchwork.freedesktop.org/patch/msgid/20161117210411.14044-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -4554,6 +4554,11 @@ void i915_gem_load_cleanup(struct drm_device *dev)
 
 	WARN_ON(!llist_empty(&dev_priv->mm.free_list));
 
+	mutex_lock(&dev_priv->drm.struct_mutex);
+	i915_gem_timeline_fini(&dev_priv->gt.global_timeline);
+	WARN_ON(!list_empty(&dev_priv->gt.timelines));
+	mutex_unlock(&dev_priv->drm.struct_mutex);
+
 	kmem_cache_destroy(dev_priv->dependencies);
 	kmem_cache_destroy(dev_priv->requests);
 	kmem_cache_destroy(dev_priv->vmas);