memcg: fix try_get_mem_cgroup_from_swapcache()

This is a bugfix for commit 3c776e6 ("memcg: charge swapcache to proper memcg"). Used bit of swapcache is solid under page lock, but considering move_account, pc->mem_cgroup is not. We need lock_page_cgroup() anyway. Signed-off-by: Daisuke Nishimura <[email protected]> Acked-by: KAMEZAWA Hiroyuki <[email protected]> Cc: Balbir Singh <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
rtvt123 · May 2, 2009 · c0bd3f6 · c0bd3f6
1 parent 1e50cc9
commit c0bd3f6
Showing 1 changed file with 2 additions and 3 deletions.
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
@@ -1024,9 +1024,7 @@ static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page)
 		return NULL;
 
 	pc = lookup_page_cgroup(page);
-	/*
-	 * Used bit of swapcache is solid under page lock.
-	 */
+	lock_page_cgroup(pc);
 	if (PageCgroupUsed(pc)) {
 		mem = pc->mem_cgroup;
 		if (mem && !css_tryget(&mem->css))
@@ -1040,6 +1038,7 @@ static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page)
 			mem = NULL;
 		rcu_read_unlock();
 	}
+	unlock_page_cgroup(pc);
 	return mem;
 }