On 5/6/21 12:00 PM, Vlastimil Babka wrote:
On 5/5/21 10:06 PM, Waiman Long wrote:
There are currently two problems in the way the objcg pointer array
(memcg_data) in the page structure is being allocated and freed.
On its allocation, it is possible that the allocated objcg pointer
array comes from the same slab that requires memory accounting. If this
happens, the slab will never become empty again as there is at least
one object left (the obj_cgroup array) in the slab.
When it is freed, the objcg pointer array object may be the last one
in its slab and hence causes kfree() to be called again. With the
right workload, the slab cache may be set up in a way that allows the
recursive kfree() calling loop to nest deep enough to cause a kernel
stack overflow and panic the system.
One way to solve this problem is to split the kmalloc-<n> caches
(KMALLOC_NORMAL) into two separate sets - a new set of kmalloc-<n>
(KMALLOC_NORMAL) caches for unaccounted objects only and a new set of
kmalloc-cg-<n> (KMALLOC_CGROUP) caches for accounted objects only. All
the other caches can still allow a mix of accounted and unaccounted
objects.
With this change, all the objcg pointer array objects will come from
KMALLOC_NORMAL caches which won't have their objcg pointer arrays. So
both the recursive kfree() problem and non-freeable slab problem are
gone.
Since both the KMALLOC_NORMAL and KMALLOC_CGROUP caches no longer have
mixed accounted and unaccounted objects, this will slightly reduce the
number of objcg pointer arrays that need to be allocated and save a bit
of memory. On the other hand, creating a new set of kmalloc caches does
have the effect of reducing cache utilization. So it is properly a wash.
The new KMALLOC_CGROUP is added between KMALLOC_NORMAL and
KMALLOC_RECLAIM so that the first for loop in create_kmalloc_caches()
will include the newly added caches without change.
Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
I still believe the cgroup.memory=nokmem parameter should be respected,
otherwise the caches are not only created, but also used. I offer this followup
for squashing into your patch if you and Andrew agree:
----8<----
From c87378d437d9a59b8757033485431b4721c74173 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@xxxxxxx>
Date: Thu, 6 May 2021 17:53:21 +0200
Subject: [PATCH] mm: memcg/slab: don't create kmalloc-cg caches with
cgroup.memory=nokmem
The caches should not be created when kmemcg is disabled on boot, otherwise
they are also filled by kmalloc(__GFP_ACCOUNT) allocations. When booted with
cgroup.memory=nokmem, link the kmalloc_caches[KMALLOC_CGROUP] entries to
KMALLOC_NORMAL entries instead.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
mm/internal.h | 5 +++++
mm/memcontrol.c | 2 +-
mm/slab_common.c | 9 +++++++--
3 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/mm/internal.h b/mm/internal.h
index ef5f336f59bd..b2d60b3403c7 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -135,6 +135,11 @@ extern void putback_lru_page(struct page *page);
*/
extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);
+/*
+ * in mm/memcontrol.c:
+ */
+extern bool cgroup_memory_nokmem;
+
/*
* in mm/page_alloc.c
*/
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5e3b4f23b830..b9ec01f2b4f6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -83,7 +83,7 @@ DEFINE_PER_CPU(struct mem_cgroup *, int_active_memcg);
static bool cgroup_memory_nosocket;
/* Kernel memory accounting disabled? */
-static bool cgroup_memory_nokmem;
+bool cgroup_memory_nokmem;
/* Whether the swap controller is active */
#ifdef CONFIG_MEMCG_SWAP
diff --git a/mm/slab_common.c b/mm/slab_common.c
index bbaf41a7c77e..363f90215401 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -832,10 +832,15 @@ void __init setup_kmalloc_cache_index_table(void)
static void __init
new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
{
- if (type == KMALLOC_RECLAIM)
+ if (type == KMALLOC_RECLAIM) {
flags |= SLAB_RECLAIM_ACCOUNT;
- else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP))
+ } else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP)) {
+ if (cgroup_memory_nokmem) {
+ kmalloc_caches[type][idx] = kmalloc_caches[KMALLOC_NORMAL][idx];
+ return;
+ }
flags |= SLAB_ACCOUNT;
+ }
kmalloc_caches[type][idx] = create_kmalloc_cache(
kmalloc_info[idx].name[type],
Thanks, the patch looks good to me.
Acked-by: Waiman Long <longman@xxxxxxxxxx>
Cheers,
Longman
