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On 5/14/19 8:06 PM, Shakeel Butt wrote:
@@ -2651,20 +2652,35 @@ struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
struct mem_cgroup *memcg;
struct kmem_cache *memcg_cachep;
int kmemcg_id;
+ struct memcg_cache_array *arr;
VM_BUG_ON(!is_root_cache(cachep));
if (memcg_kmem_bypass())
return cachep;
- memcg = get_mem_cgroup_from_current();
+ rcu_read_lock();
+
+ if (unlikely(current->active_memcg))
+ memcg = current->active_memcg;
+ else
+ memcg = mem_cgroup_from_task(current);
+
+ if (!memcg || memcg == root_mem_cgroup)
+ goto out_unlock;
+
kmemcg_id = READ_ONCE(memcg->kmemcg_id);
if (kmemcg_id < 0)
- goto out;
+ goto out_unlock;
- memcg_cachep = cache_from_memcg_idx(cachep, kmemcg_id);
- if (likely(memcg_cachep))
- return memcg_cachep;
+ arr = rcu_dereference(cachep->memcg_params.memcg_caches);
+
+ /*
+ * Make sure we will access the up-to-date value. The code updating
+ * memcg_caches issues a write barrier to match this (see
+ * memcg_create_kmem_cache()).
+ */
+ memcg_cachep = READ_ONCE(arr->entries[kmemcg_id]);
/*
* If we are in a safe context (can wait, and not in interrupt
@@ -2677,10 +2693,20 @@ struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
* memcg_create_kmem_cache, this means no further allocation
* could happen with the slab_mutex held. So it's better to
* defer everything.
+ *
+ * If the memcg is dying or memcg_cache is about to be released,
+ * don't bother creating new kmem_caches. Because memcg_cachep
+ * is ZEROed as the fist step of kmem offlining, we don't need
+ * percpu_ref_tryget() here. css_tryget_online() check in
*percpu_ref_tryget_live()
+ * memcg_schedule_kmem_cache_create() will prevent us from
+ * creation of a new kmem_cache.
*/
- memcg_schedule_kmem_cache_create(memcg, cachep);
-out:
- css_put(&memcg->css);
+ if (unlikely(!memcg_cachep))
+ memcg_schedule_kmem_cache_create(memcg, cachep);
+ else if (percpu_ref_tryget(&memcg_cachep->memcg_params.refcnt))
+ cachep = memcg_cachep;
+out_unlock:
+ rcu_read_lock();
There is one more bug that causes the kernel to panic on bootup
when I turned on debugging options.
[ 49.871437] =============================
[ 49.875452] WARNING: suspicious RCU usage
[ 49.879476] 5.2.0-rc1.bz1699202_memcg_test+ #2 Not tainted
[ 49.884967] -----------------------------
[ 49.888991] include/linux/rcupdate.h:268 Illegal context switch
in RCU read-side critical section!
[ 49.897950]
[ 49.897950] other info that might help us debug this:
[ 49.897950]
[ 49.905958]
[ 49.905958] rcu_scheduler_active = 2, debug_locks = 1
[ 49.912492] 3 locks held by systemd/1:
[ 49.916252] #0: 00000000633673c5
(&type->i_mutex_dir_key#5){.+.+}, at: lookup_slow+0x42/0x70
[ 49.924788] #1: 0000000029fa8c75 (rcu_read_lock){....}, at:
memcg_kmem_get_cache+0x12b/0x910
[ 49.933316] #2: 0000000029fa8c75 (rcu_read_lock){....}, at:
memcg_kmem_get_cache+0x3da/0x910
It should be "rcu_read_unlock();" at the end.
-Longman
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