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Subject: Re: WARNING bisected (was Re: [PATCH v7 08/10] mm: rework non-root
 kmem_cache lifecycle management)
To:     Roman Gushchin <guro@fb.com>
Cc:     "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "hannes@cmpxchg.org" <hannes@cmpxchg.org>,
        Kernel Team <Kernel-team@fb.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "longman@redhat.com" <longman@redhat.com>,
        "shakeelb@google.com" <shakeelb@google.com>,
        "vdavydov.dev@gmail.com" <vdavydov.dev@gmail.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
References: <20190611231813.3148843-9-guro@fb.com>
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From:   Christian Borntraeger <borntraeger@de.ibm.com>
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Date:   Mon, 25 Nov 2019 09:00:56 +0100
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On 24.11.19 01:39, Roman Gushchin wrote:
> On Fri, Nov 22, 2019 at 05:28:46PM +0100, Christian Borntraeger wrote:
>> On 21.11.19 19:45, Roman Gushchin wrote:
>>> I see. Do you know, which kmem_cache it is? If not, can you, please,
>>> figure it out?
>>
>> The release function for that ref is kmemcg_cache_shutdown. 
>>
> 
> Hi Christian!
> 
> Can you, please, test if the following patch resolves the problem?

Yes, it does.


> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 8afa188f6e20..628e5f0ee19e 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -888,6 +888,8 @@ static int shutdown_memcg_caches(struct kmem_cache *s)
>  
>  static void flush_memcg_workqueue(struct kmem_cache *s)
>  {
> +	bool wait_for_children;
> +
>  	spin_lock_irq(&memcg_kmem_wq_lock);
>  	s->memcg_params.dying = true;
>  	spin_unlock_irq(&memcg_kmem_wq_lock);
> @@ -904,6 +906,13 @@ static void flush_memcg_workqueue(struct kmem_cache *s)
>  	 * previous workitems on workqueue are processed.
>  	 */
>  	flush_workqueue(memcg_kmem_cache_wq);
> +
> +	mutex_lock(&slab_mutex);
> +	wait_for_children = !list_empty(&s->memcg_params.children);
> +	mutex_unlock(&slab_mutex);

Not sure if (for reading) we really need the mutex. 
> +
> +	if (wait_for_children)
> +		rcu_barrier();
>  }
>  #else
>  static inline int shutdown_memcg_caches(struct kmem_cache *s)
> 
> --
> 
> Thanks!
>