[patch 03/10] mm/memcontrol: fix warning in mem_cgroup_page_lruvec()

[Andrew Morton <akpm@linux-foundation.org>]

From: Hugh Dickins <hughd@google.com>
Subject: mm/memcontrol: fix warning in mem_cgroup_page_lruvec()

Boot a CONFIG_MEMCG=y kernel with "cgroup_disabled=memory" and you are met
by a series of warnings from the VM_WARN_ON_ONCE_PAGE(!memcg, page)
recently added to the inline mem_cgroup_page_lruvec().

An earlier attempt to place that warning, in mem_cgroup_lruvec(), had been
careful to do so after weeding out the mem_cgroup_disabled() case; but was
itself invalid because of the mem_cgroup_lruvec(NULL, pgdat) in
clear_pgdat_congested() and age_active_anon().

Warning in mem_cgroup_page_lruvec() was once useful in detecting a KSM
charge bug, so may be worth keeping: but skip if mem_cgroup_disabled().

Link: https://lkml.kernel.org/r/alpine.LSU.2.11.2101032056260.1093@eggly.anvils
Fixes: 9a1ac2288cf1 ("mm/memcontrol:rewrite mem_cgroup_page_lruvec()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Alex Shi <alex.shi@linux.alibaba.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Chris Down <chris@chrisdown.name>
Reviewed-by: Baoquan He <bhe@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hui Su <sh_def@163.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/memcontrol.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/memcontrol.h~mm-memcontrol-fix-warning-in-mem_cgroup_page_lruvec
+++ a/include/linux/memcontrol.h
@@ -665,7 +665,7 @@ static inline struct lruvec *mem_cgroup_
 {
 	struct mem_cgroup *memcg = page_memcg(page);
 
-	VM_WARN_ON_ONCE_PAGE(!memcg, page);
+	VM_WARN_ON_ONCE_PAGE(!memcg && !mem_cgroup_disabled(), page);
 	return mem_cgroup_lruvec(memcg, pgdat);
 }
 
_