[-resend,v2] memcg: make it work on sparse non-0-node systems

Commit Message

Jiri Slaby May 22, 2019, 9:19 a.m. UTC

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.

[v2] use the idea proposed by Vladimir -- the bool flag.

Signed-off-by: Jiri Slaby <[e-mail]>
Fixes: 60d3fd32a7a9 ("list_lru: introduce per-memcg lists")
Cc: Johannes Weiner <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Suggested-by: Vladimir Davydov <[e-mail]>
Acked-by: Vladimir Davydov <[e-mail]>
Reviewed-by: Shakeel Butt <[e-mail]>
Cc: <[e-mail]>
Cc: <[e-mail]>
Cc: <[e-mail]>
Cc: Raghavendra K T <[e-mail]>
---

This is only a resent patch. I did not send it the akpm's way previously.

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

Comments

Sasha Levin May 29, 2019, 1:14 p.m. UTC | #1

Hi,

[This is an automated email]

This commit has been processed because it contains a "Fixes:" tag,
fixing commit: 60d3fd32a7a9d list_lru: introduce per-memcg lists.

The bot has tested the following trees: v5.1.4, v5.0.18, v4.19.45, v4.14.121, v4.9.178, v4.4.180.

v5.1.4: Build OK!
v5.0.18: Build OK!
v4.19.45: Build OK!
v4.14.121: Failed to apply! Possible dependencies:
    0200894d11551 ("new helper: destroy_unused_super()")
    2b3648a6ff83b ("fs/super.c: refactor alloc_super()")
    39887653aab4c ("mm/workingset.c: refactor workingset_init()")
    8e04944f0ea8b ("mm,vmscan: Allow preallocating memory for register_shrinker().")
    c92e8e10cafea ("fs: propagate shrinker::id to list_lru")

v4.9.178: Failed to apply! Possible dependencies:
    0200894d11551 ("new helper: destroy_unused_super()")
    14b468791fa95 ("mm: workingset: move shadow entry tracking to radix tree exceptional tracking")
    2b3648a6ff83b ("fs/super.c: refactor alloc_super()")
    39887653aab4c ("mm/workingset.c: refactor workingset_init()")
    4d693d08607ab ("lib: radix-tree: update callback for changing leaf nodes")
    6d75f366b9242 ("lib: radix-tree: check accounting of existing slot replacement users")
    8e04944f0ea8b ("mm,vmscan: Allow preallocating memory for register_shrinker().")
    c92e8e10cafea ("fs: propagate shrinker::id to list_lru")
    f4b109c6dad54 ("lib: radix-tree: add entry deletion support to __radix_tree_replace()")
    f7942430e40f1 ("lib: radix-tree: native accounting of exceptional entries")

v4.4.180: Failed to apply! Possible dependencies:
    0200894d11551 ("new helper: destroy_unused_super()")
    0cefabdaf757a ("mm: workingset: fix premature shadow node shrinking with cgroups")
    0e749e54244ee ("dax: increase granularity of dax_clear_blocks() operations")
    14b468791fa95 ("mm: workingset: move shadow entry tracking to radix tree exceptional tracking")
    162453bfbdf4c ("mm: workingset: separate shadow unpacking and refault calculation")
    2b3648a6ff83b ("fs/super.c: refactor alloc_super()")
    39887653aab4c ("mm/workingset.c: refactor workingset_init()")
    52db400fcd502 ("pmem, dax: clean up clear_pmem()")
    612e44939c3c7 ("mm: workingset: eviction buckets for bigmem/lowbit machines")
    689c94f03ae25 ("mm: workingset: #define radix entry eviction mask")
    6e4eab577a0ca ("fs: Add user namespace member to struct super_block")
    8e04944f0ea8b ("mm,vmscan: Allow preallocating memory for register_shrinker().")
    ac401cc782429 ("dax: New fault locking")
    b2e0d1625e193 ("dax: fix lifetime of in-kernel dax mappings with dax_map_atomic()")
    c92e8e10cafea ("fs: propagate shrinker::id to list_lru")
    d91ee87d8d85a ("vfs: Pass data, ns, and ns->userns to mount_ns")
    e4b2749158631 ("DAX: move RADIX_DAX_ definitions to dax.c")
    f7942430e40f1 ("lib: radix-tree: native accounting of exceptional entries")
    f9fe48bece3af ("dax: support dirty DAX entries in radix tree")


How should we proceed with this patch?

--
Thanks,
Sasha

Patch

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index aa5efd9351eb..d5ceb2839a2d 100644
--- a/include/linux/list_lru.h
+++ b/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
 };
 
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 0730bf8ff39f..d3b538146efd 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -37,11 +37,7 @@  static int lru_shrinker_id(struct list_lru *lru)
 
 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 list_lru *lru, bool memcg_aware)
 {
 	int i;
 
+	lru->memcg_aware = memcg_aware;
+
 	if (!memcg_aware)
 		return 0;