The patch titled
Subject: memcg: make it work on sparse non-0-node systems
has been added to the -mm tree. Its filename is
memcg-make-it-work-on-sparse-non-0-node-systems.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/memcg-make-it-work-on-sparse-non-0-node-systems.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/memcg-make-it-work-on-sparse-non-0-node-systems.patch
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From: Jiri Slaby <jslaby@xxxxxxx>
Subject: memcg: make it work on sparse non-0-node systems
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:
d_lru_add+0x44/0x50
dput.part.34+0xfc/0x110
__fput+0x108/0x230
task_work_run+0x9f/0xc0
exit_to_usermode_loop+0xf5/0x100
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>
---
include/linux/list_lru.h | 1 +
mm/list_lru.c | 8 +++-----
2 files changed, 4 insertions(+), 5 deletions(-)
--- a/include/linux/list_lru.h~memcg-make-it-work-on-sparse-non-0-node-systems
+++ a/include/linux/list_lru.h
@@ -54,6 +54,7 @@ struct list_lru {
#ifdef CONFIG_MEMCG_KMEM
struct list_head list;
int shrinker_id;
+ bool memcg_aware;
#endif
};
--- a/mm/list_lru.c~memcg-make-it-work-on-sparse-non-0-node-systems
+++ a/mm/list_lru.c
@@ -37,11 +37,7 @@ static int lru_shrinker_id(struct list_l
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 *
@@ -451,6 +447,8 @@ static int memcg_init_list_lru(struct li
{
int i;
+ lru->memcg_aware = memcg_aware;
+
if (!memcg_aware)
return 0;
_
Patches currently in -mm which might be from jslaby@xxxxxxx are
memcg-make-it-work-on-sparse-non-0-node-systems.patch
