drn/i915: Break up long i915_buddy_free_list() with a cond_resched()

In the selftests, we may feed very long lists of blocks to be freed on
culmination of the tests. This coupled with kasan and other
malloc-tracing can make the kmem_cache_free() operation time consuming,
and doing many of those trigger soft lockup warnings. Break the list up
with a cond_resched().
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191221144917.1040662-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_buddy.c

@@ -262,8 +262,10 @@ void i915_buddy_free_list(struct i915_buddy_mm *mm, struct list_head *objects)
 {
 	struct i915_buddy_block *block, *on;
 
-	list_for_each_entry_safe(block, on, objects, link)
+	list_for_each_entry_safe(block, on, objects, link) {
 		i915_buddy_free(mm, block);
+		cond_resched();
+	}
 	INIT_LIST_HEAD(objects);
 }