drm/ttm: fix re-init of global structures

When a driver unloads without unloading TTM we don't correctly
clear the global structures leading to errors on re-init.

Next step should probably be to remove the global structures and
kobjs all together, but this is tricky since we need to maintain
backward compatibility.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Tested-by: Karol Herbst <kherbst@redhat.com>
CC: stable@vger.kernel.org # 5.0.x
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -49,9 +49,8 @@ static void ttm_bo_global_kobj_release(struct kobject *kobj);
  * ttm_global_mutex - protecting the global BO state
  */
 DEFINE_MUTEX(ttm_global_mutex);
-struct ttm_bo_global ttm_bo_glob = {
-	.use_count = 0
-};
+unsigned ttm_bo_glob_use_count;
+struct ttm_bo_global ttm_bo_glob;
 
 static struct attribute ttm_bo_count = {
 	.name = "bo_count",
@@ -1531,12 +1530,13 @@ static void ttm_bo_global_release(void)
 	struct ttm_bo_global *glob = &ttm_bo_glob;
 
 	mutex_lock(&ttm_global_mutex);
-	if (--glob->use_count > 0)
+	if (--ttm_bo_glob_use_count > 0)
 		goto out;
 
 	kobject_del(&glob->kobj);
 	kobject_put(&glob->kobj);
 	ttm_mem_global_release(&ttm_mem_glob);
+	memset(glob, 0, sizeof(*glob));
 out:
 	mutex_unlock(&ttm_global_mutex);
 }
@@ -1548,7 +1548,7 @@ static int ttm_bo_global_init(void)
 	unsigned i;
 
 	mutex_lock(&ttm_global_mutex);
-	if (++glob->use_count > 1)
+	if (++ttm_bo_glob_use_count > 1)
 		goto out;
 
 	ret = ttm_mem_global_init(&ttm_mem_glob);

drivers/gpu/drm/ttm/ttm_memory.c

@@ -461,8 +461,8 @@ int ttm_mem_global_init(struct ttm_mem_global *glob)
 
 void ttm_mem_global_release(struct ttm_mem_global *glob)
 {
-	unsigned int i;
 	struct ttm_mem_zone *zone;
+	unsigned int i;
 
 	/* let the page allocator first stop the shrink work. */
 	ttm_page_alloc_fini();
@@ -478,6 +478,7 @@ void ttm_mem_global_release(struct ttm_mem_global *glob)
 	}
 	kobject_del(&glob->kobj);
 	kobject_put(&glob->kobj);
+	memset(glob, 0, sizeof(*glob));
 }
 
 static void ttm_check_swapping(struct ttm_mem_global *glob)

include/drm/ttm/ttm_bo_driver.h

@@ -420,7 +420,6 @@ extern struct ttm_bo_global {
 	/**
 	 * Protected by ttm_global_mutex.
 	 */
-	unsigned int use_count;
 	struct list_head device_list;
 
 	/**