drm/selftests/mm: Insert cond_resched() between insert modes

kbuilder has begun running the selftests and reported a soft-lockup
inside __igt_insert(), so break up the test loop over different modes
with another call to cond_resched().
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171107104131.5923-1-chris@chris-wilson.co.uk

drivers/gpu/drm/selftests/test-drm_mm.c

@@ -682,6 +682,8 @@ static int __igt_insert(unsigned int count, u64 size, bool replace)
 		drm_mm_for_each_node_safe(node, next, &mm)
 			drm_mm_remove_node(node);
 		DRM_MM_BUG_ON(!drm_mm_clean(&mm));
+
+		cond_resched();
 	}
 
 	ret = 0;
@@ -944,6 +946,8 @@ static int __igt_insert_range(unsigned int count, u64 size, u64 start, u64 end)
 		drm_mm_for_each_node_safe(node, next, &mm)
 			drm_mm_remove_node(node);
 		DRM_MM_BUG_ON(!drm_mm_clean(&mm));
+
+		cond_resched();
 	}
 
 	ret = 0;
@@ -1068,6 +1072,7 @@ static int igt_align(void *ignored)
 		drm_mm_for_each_node_safe(node, next, &mm)
 			drm_mm_remove_node(node);
 		DRM_MM_BUG_ON(!drm_mm_clean(&mm));
+
 		cond_resched();
 	}