From: Jiri Slaby jslaby@suse.cz 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@suse.cz Fixes: 60d3fd32a7a9 ("list_lru: introduce per-memcg lists") Signed-off-by: Jiri Slaby jslaby@suse.cz Acked-by: Michal Hocko mhocko@suse.com Suggested-by: Vladimir Davydov vdavydov.dev@gmail.com Acked-by: Vladimir Davydov vdavydov.dev@gmail.com Reviewed-by: Shakeel Butt shakeelb@google.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Raghavendra K T raghavendra.kt@linux.vnet.ibm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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 @@ -38,11 +38,7 @@ 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 * @@ -452,6 +448,8 @@ static int memcg_init_list_lru(struct li { int i;

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

_