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Date: Fri, 8 Jun 2018 13:35:52 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Shakeel Butt <shakeelb@...gle.com>
Cc: Michal Hocko <mhocko@...nel.org>, Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Greg Thelen <gthelen@...gle.com>,
Johannes Weiner <hannes@...xchg.org>,
Vladimir Davydov <vdavydov.dev@...il.com>,
Tejun Heo <tj@...nel.org>, Linux MM <linux-mm@...ck.org>,
Cgroups <cgroups@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] mm: fix race between kmem_cache destroy, create and
deactivate
On Tue, 29 May 2018 17:12:04 -0700 Shakeel Butt <shakeelb@...gle.com> wrote:
> The memcg kmem cache creation and deactivation (SLUB only) is
> asynchronous. If a root kmem cache is destroyed whose memcg cache is in
> the process of creation or deactivation, the kernel may crash.
>
> Example of one such crash:
> general protection fault: 0000 [#1] SMP PTI
> CPU: 1 PID: 1721 Comm: kworker/14:1 Not tainted 4.17.0-smp
> ...
> Workqueue: memcg_kmem_cache kmemcg_deactivate_workfn
> RIP: 0010:has_cpu_slab
> ...
> Call Trace:
> ? on_each_cpu_cond
> __kmem_cache_shrink
> kmemcg_cache_deact_after_rcu
> kmemcg_deactivate_workfn
> process_one_work
> worker_thread
> kthread
> ret_from_fork+0x35/0x40
>
> To fix this race, on root kmem cache destruction, mark the cache as
> dying and flush the workqueue used for memcg kmem cache creation and
> deactivation.
We have a distinct lack of reviewers and testers on this one. Please.
Vladimir, v3 replaced the refcounting with workqueue flushing, as you
suggested...
From: Shakeel Butt <shakeelb@...gle.com>
Subject: mm: fix race between kmem_cache destroy, create and deactivate
The memcg kmem cache creation and deactivation (SLUB only) is
asynchronous. If a root kmem cache is destroyed whose memcg cache is in
the process of creation or deactivation, the kernel may crash.
Example of one such crash:
general protection fault: 0000 [#1] SMP PTI
CPU: 1 PID: 1721 Comm: kworker/14:1 Not tainted 4.17.0-smp
...
Workqueue: memcg_kmem_cache kmemcg_deactivate_workfn
RIP: 0010:has_cpu_slab
...
Call Trace:
? on_each_cpu_cond
__kmem_cache_shrink
kmemcg_cache_deact_after_rcu
kmemcg_deactivate_workfn
process_one_work
worker_thread
kthread
ret_from_fork+0x35/0x40
To fix this race, on root kmem cache destruction, mark the cache as dying
and flush the workqueue used for memcg kmem cache creation and
deactivation.
[shakeelb@...gle.com: add more documentation, rename fields for readability]
Link: http://lkml.kernel.org/r/20180522201336.196994-1-shakeelb@google.com
[akpm@...ux-foundation.org: fix build, per Shakeel]
[shakeelb@...gle.com: v3. Instead of refcount, flush the workqueue]
Link: http://lkml.kernel.org/r/20180530001204.183758-1-shakeelb@google.com
Link: http://lkml.kernel.org/r/20180521174116.171846-1-shakeelb@google.com
Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Greg Thelen <gthelen@...gle.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Pekka Enberg <penberg@...nel.org>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: Tejun Heo <tj@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
include/linux/slab.h | 1 +
mm/slab_common.c | 21 ++++++++++++++++++++-
2 files changed, 21 insertions(+), 1 deletion(-)
diff -puN include/linux/slab_def.h~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate include/linux/slab_def.h
diff -puN include/linux/slab.h~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate include/linux/slab.h
--- a/include/linux/slab.h~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate
+++ a/include/linux/slab.h
@@ -600,6 +600,7 @@ struct memcg_cache_params {
struct memcg_cache_array __rcu *memcg_caches;
struct list_head __root_caches_node;
struct list_head children;
+ bool dying;
};
struct {
struct mem_cgroup *memcg;
diff -puN include/linux/slub_def.h~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate include/linux/slub_def.h
diff -puN mm/memcontrol.c~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate mm/memcontrol.c
diff -puN mm/slab.c~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate mm/slab.c
diff -puN mm/slab_common.c~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate mm/slab_common.c
--- a/mm/slab_common.c~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate
+++ a/mm/slab_common.c
@@ -136,6 +136,7 @@ void slab_init_memcg_params(struct kmem_
s->memcg_params.root_cache = NULL;
RCU_INIT_POINTER(s->memcg_params.memcg_caches, NULL);
INIT_LIST_HEAD(&s->memcg_params.children);
+ s->memcg_params.dying = false;
}
static int init_memcg_params(struct kmem_cache *s,
@@ -608,7 +609,7 @@ void memcg_create_kmem_cache(struct mem_
* The memory cgroup could have been offlined while the cache
* creation work was pending.
*/
- if (memcg->kmem_state != KMEM_ONLINE)
+ if (memcg->kmem_state != KMEM_ONLINE || root_cache->memcg_params.dying)
goto out_unlock;
idx = memcg_cache_id(memcg);
@@ -712,6 +713,9 @@ void slab_deactivate_memcg_cache_rcu_sch
WARN_ON_ONCE(s->memcg_params.deact_fn))
return;
+ if (s->memcg_params.root_cache->memcg_params.dying)
+ return;
+
/* pin memcg so that @s doesn't get destroyed in the middle */
css_get(&s->memcg_params.memcg->css);
@@ -823,11 +827,24 @@ static int shutdown_memcg_caches(struct
return -EBUSY;
return 0;
}
+
+static void flush_memcg_workqueue(struct kmem_cache *s)
+{
+ mutex_lock(&slab_mutex);
+ s->memcg_params.dying = true;
+ mutex_unlock(&slab_mutex);
+
+ flush_workqueue(memcg_kmem_cache_wq);
+}
#else
static inline int shutdown_memcg_caches(struct kmem_cache *s)
{
return 0;
}
+
+static inline void flush_memcg_workqueue(struct kmem_cache *s)
+{
+}
#endif /* CONFIG_MEMCG && !CONFIG_SLOB */
void slab_kmem_cache_release(struct kmem_cache *s)
@@ -845,6 +862,8 @@ void kmem_cache_destroy(struct kmem_cach
if (unlikely(!s))
return;
+ flush_memcg_workqueue(s);
+
get_online_cpus();
get_online_mems();
diff -puN mm/slab.h~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate mm/slab.h
diff -puN mm/slub.c~mm-fix-race-between-kmem_cache-destroy-create-and-deactivate mm/slub.c
_
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