drm/msm: Fix error handling crashes seen when VRAM allocation fails

If VRAM allocation fails, the error handling path crashes in
msm_drm_uninit(). The following changes are made to fix this:

msm_gem_shrinker_cleanup() is fixed to unregister the shrinker only
if it was init-ed in the first place.

Before calling kms->funcs->destroy(), we check if kms->funcs is also
non-NULL. This is needed for MDP5, since during msm_drm_int(), priv->kms
becomes non-NULL early, but msm_kms_init() is called on it only later
in mdp5_kms_init().
Signed-off-by: NArchit Taneja <architt@codeaurora.org>
Signed-off-by: NRob Clark <robdclark@gmail.com>
Reviewed-by: NAndy Gross <andy.gross@linaro.org>

drivers/gpu/drm/msm/msm_drv.c

@@ -228,7 +228,7 @@ static int msm_drm_uninit(struct device *dev)
 	flush_workqueue(priv->atomic_wq);
 	destroy_workqueue(priv->atomic_wq);
 
-	if (kms)
+	if (kms && kms->funcs)
 		kms->funcs->destroy(kms);
 
 	if (gpu) {

drivers/gpu/drm/msm/msm_gem_shrinker.c

@@ -163,6 +163,9 @@ void msm_gem_shrinker_init(struct drm_device *dev)
 void msm_gem_shrinker_cleanup(struct drm_device *dev)
 {
 	struct msm_drm_private *priv = dev->dev_private;
+
+	if (priv->shrinker.nr_deferred) {
 		WARN_ON(unregister_vmap_purge_notifier(&priv->vmap_notifier));
 		unregister_shrinker(&priv->shrinker);
+	}
 }