memcg: fix try_get_mem_cgroup_from_swapcache()
This is a bugfix for commit 3c776e64660028236313f0e54f3a9945764422df
("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 <nishimura@mxp.nes.nec.co.jp>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e44fb0f..575203a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1024,9 +1024,7 @@
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 @@
mem = NULL;
rcu_read_unlock();
}
+ unlock_page_cgroup(pc);
return mem;
}
