[PATCH 4.9 42/83] memcg: make it work on sparse non-0-node systems

From: Greg Kroah-Hartman
Date: Sun Jun 09 2019 - 13:20:52 EST

From: Jiri Slaby <jslaby@xxxxxxx>

commit 3e8589963773a5c23e2f1fe4bcad0e9a90b7f471 upstream.

We have a single node system with node 0 disabled:
Scanning NUMA topology in Northbridge 24
Number of physical nodes 2
Skipping disabled node 0
Node 1 MemBase 0000000000000000 Limit 00000000fbff0000
NODE_DATA(1) allocated [mem 0xfbfda000-0xfbfeffff]

This causes crashes in memcg when system boots:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
#PF error: [normal kernel read fault]
RIP: 0010:list_lru_add+0x94/0x170
Call Trace:

It is reproducible as far as 4.12. I did not try older kernels. You have
to have a new enough systemd, e.g. 241 (the reason is unknown -- was not
investigated). Cannot be reproduced with systemd 234.

The system crashes because the size of lru array is never updated in
memcg_update_all_list_lrus and the reads are past the zero-sized array,
causing dereferences of random memory.

The root cause are list_lru_memcg_aware checks in the list_lru code. The
test in list_lru_memcg_aware is broken: it assumes node 0 is always
present, but it is not true on some systems as can be seen above.

So fix this by avoiding checks on node 0. Remember the memcg-awareness by
a bool flag in struct list_lru.

Link: http://lkml.kernel.org/r/20190522091940.3615-1-jslaby@xxxxxxx
Fixes: 60d3fd32a7a9 ("list_lru: introduce per-memcg lists")
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Suggested-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

include/linux/list_lru.h | 1 +
mm/list_lru.c | 8 +++-----
2 files changed, 4 insertions(+), 5 deletions(-)

--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -51,6 +51,7 @@ struct list_lru {
struct list_lru_node *node;
#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
struct list_head list;
+ bool memcg_aware;

--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -42,11 +42,7 @@ static void list_lru_unregister(struct l
#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
static inline bool list_lru_memcg_aware(struct list_lru *lru)
- /*
- * This needs node 0 to be always present, even
- * in the systems supporting sparse numa ids.
- */
- return !!lru->node[0].memcg_lrus;
+ return lru->memcg_aware;

static inline struct list_lru_one *
@@ -389,6 +385,8 @@ static int memcg_init_list_lru(struct li
int i;

+ lru->memcg_aware = memcg_aware;
if (!memcg_aware)
return 0;