mm/memcg: set memcg after css verified and got reference

Patch series "mm/memcg: some cleanup for mem_cgroup_iter()", v2.

No functional change, try to make it more readable.


This patch (of 3):

Instead of resetting memcg when css is either not verified or not got
reference, we can set it after these process.

No functional change, just simplified the code a little.

Link: https://lkml.kernel.org/r/20220330234719.18340-1-richard.weiyang@gmail.com
Link: https://lkml.kernel.org/r/20220330234719.18340-2-richard.weiyang@gmail.comSigned-off-by: Wei Yang <richard.weiyang@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memcontrol.c

@@ -1065,15 +1065,10 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
 		 * is provided by the caller, so we know it's alive
 		 * and kicking, and don't take an extra reference.
 		 */
-		memcg = mem_cgroup_from_css(css);
-
-		if (css == &root->css)
-			break;
-
-		if (css_tryget(css))
+		if (css == &root->css || css_tryget(css)) {
+			memcg = mem_cgroup_from_css(css);
 			break;
-
-		memcg = NULL;
+		}
 	}
 
 	if (reclaim) {