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From: Johannes Weiner <hannes@cmpxchg.org>
To: Muchun Song <songmuchun@bytedance.com>
Cc: guro@fb.com, mhocko@kernel.org, akpm@linux-foundation.org,
	shakeelb@google.com, vdavydov.dev@gmail.com,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	duanxiongchun@bytedance.com
Subject: Re: [PATCH v5 1/7] mm: memcontrol: slab: fix obtain a reference to a freeing memcg
Date: Mon, 22 Mar 2021 10:46:26 -0400	[thread overview]
Message-ID: <YFitwmmLFA24cofE@cmpxchg.org> (raw)
In-Reply-To: <20210319163821.20704-2-songmuchun@bytedance.com>

On Sat, Mar 20, 2021 at 12:38:14AM +0800, Muchun Song wrote:
> The rcu_read_lock/unlock only can guarantee that the memcg will not be
> freed, but it cannot guarantee the success of css_get (which is in the
> refill_stock when cached memcg changed) to memcg.
> 
>   rcu_read_lock()
>   memcg = obj_cgroup_memcg(old)
>   __memcg_kmem_uncharge(memcg)
>       refill_stock(memcg)
>           if (stock->cached != memcg)
>               // css_get can change the ref counter from 0 back to 1.
>               css_get(&memcg->css)
>   rcu_read_unlock()
> 
> This fix is very like the commit:
> 
>   eefbfa7fd678 ("mm: memcg/slab: fix use after free in obj_cgroup_charge")
> 
> Fix this by holding a reference to the memcg which is passed to the
> __memcg_kmem_uncharge() before calling __memcg_kmem_uncharge().
> 
> Fixes: 3de7d4f25a74 ("mm: memcg/slab: optimize objcg stock draining")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Good catch! Did you trigger the WARN_ON() in
percpu_ref_kill_and_confirm() during testing?


  parent reply	other threads:[~2021-03-22 14:46 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-19 16:38 [PATCH v5 0/7] Use obj_cgroup APIs to charge kmem pages Muchun Song
2021-03-19 16:38 ` [PATCH v5 1/7] mm: memcontrol: slab: fix obtain a reference to a freeing memcg Muchun Song
2021-03-19 18:26   ` Shakeel Butt
2021-03-22 14:46   ` Johannes Weiner [this message]
2021-03-23  9:18     ` [External] " Muchun Song
2021-03-22 18:17   ` Roman Gushchin
2021-03-19 16:38 ` [PATCH v5 2/7] mm: memcontrol: introduce obj_cgroup_{un}charge_pages Muchun Song
2021-03-19 16:38 ` [PATCH v5 3/7] mm: memcontrol: directly access page->memcg_data in mm/page_alloc.c Muchun Song
2021-03-19 16:38 ` [PATCH v5 4/7] mm: memcontrol: change ug->dummy_page only if memcg changed Muchun Song
2021-03-19 16:38 ` [PATCH v5 5/7] mm: memcontrol: use obj_cgroup APIs to charge kmem pages Muchun Song
2021-03-19 18:27   ` Shakeel Butt
2021-03-22 18:13   ` Roman Gushchin
2021-03-19 16:38 ` [PATCH v5 6/7] mm: memcontrol: inline __memcg_kmem_{un}charge() into obj_cgroup_{un}charge_pages() Muchun Song
2021-03-19 18:41   ` Shakeel Butt
2021-03-22 14:34   ` Johannes Weiner
2021-03-22 18:14   ` Roman Gushchin
2021-03-19 16:38 ` [PATCH v5 7/7] mm: memcontrol: move PageMemcgKmem to the scope of CONFIG_MEMCG_KMEM Muchun Song

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