@@ -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;
@@ -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 +827,36 @@ 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);
+
+ /*
+ * SLUB deactivates the kmem_caches through call_rcu_sched. Make
+ * sure all registered rcu callbacks have been invoked.
+ */
+ if (IS_ENABLED(CONFIG_SLUB))
+ rcu_barrier_sched();
+
+ /*
+ * SLAB and SLUB create memcg kmem_caches through workqueue and SLUB
+ * deactivates the memcg kmem_caches through workqueue. Make sure all
+ * previous workitems on workqueue are processed.
+ */
+ 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 +874,8 @@ void kmem_cache_destroy(struct kmem_cache *s)
if (unlikely(!s))
return;
+ flush_memcg_workqueue(s);
+
get_online_cpus();
get_online_mems();
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. SLUB's memcg kmem cache deactivation also includes RCU callback and thus make sure all previous registered RCU callbacks have completed as well. Signed-off-by: Shakeel Butt <shakeelb@google.com> --- Changelog since v3: - Handle the RCU callbacks for SLUB deactivation Changelog since v2: - Rewrote the patch and used workqueue flushing instead of refcount Changelog since v1: - Added more documentation to the code - Renamed fields to be more readable --- include/linux/slab.h | 1 + mm/slab_common.c | 33 ++++++++++++++++++++++++++++++++- 2 files changed, 33 insertions(+), 1 deletion(-)