From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f71.google.com (mail-pl0-f71.google.com [209.85.160.71]) by kanga.kvack.org (Postfix) with ESMTP id 7D79A6B0003 for ; Tue, 29 May 2018 20:12:13 -0400 (EDT) Received: by mail-pl0-f71.google.com with SMTP id 89-v6so10180532plb.18 for ; Tue, 29 May 2018 17:12:13 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id r9-v6sor13221317pfh.53.2018.05.29.17.12.11 for (Google Transport Security); Tue, 29 May 2018 17:12:11 -0700 (PDT) From: Shakeel Butt Subject: [PATCH v3] mm: fix race between kmem_cache destroy, create and deactivate Date: Tue, 29 May 2018 17:12:04 -0700 Message-Id: <20180530001204.183758-1-shakeelb@google.com> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Greg Thelen , Johannes Weiner , Vladimir Davydov , Tejun Heo Cc: Linux MM , Cgroups , LKML , Shakeel Butt 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. Signed-off-by: Shakeel Butt --- Changelog since v2: - Instead of refcount, flush the workqueue Changelog since v1: - Added more documentation to the code - Renamed fields to be more readable --- include/linux/slab.h | 1 + mm/slab_common.c | 21 ++++++++++++++++++++- 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 9ebe659bd4a5..71c5467d99c1 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -658,6 +658,7 @@ 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 --git a/mm/slab_common.c b/mm/slab_common.c index b0dd9db1eb2f..a3496375f5ea 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -136,6 +136,7 @@ void slab_init_memcg_params(struct kmem_cache *s) 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_cgroup *memcg, * 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_sched(struct kmem_cache *s, 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 kmem_cache *s) 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_cache *s) if (unlikely(!s)) return; + flush_memcg_workqueue(s); + get_online_cpus(); get_online_mems(); -- 2.17.0.921.gf22659ad46-goog