From: Muchun Song <songmuchun@bytedance.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <guro@fb.com>, Michal Hocko <mhocko@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Shakeel Butt <shakeelb@google.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux Memory Management List <linux-mm@kvack.org>,
Xiongchun duan <duanxiongchun@bytedance.com>
Subject: Re: [External] Re: [PATCH v5 1/7] mm: memcontrol: slab: fix obtain a reference to a freeing memcg
Date: Tue, 23 Mar 2021 17:18:08 +0800 [thread overview]
Message-ID: <CAMZfGtVQPonuhQOWq2D_tZyLGuBQ2auY=SF3vPJXN=iTnp8_1Q@mail.gmail.com> (raw)
In-Reply-To: <YFitwmmLFA24cofE@cmpxchg.org>
On Mon, Mar 22, 2021 at 10:46 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> 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?
No. The race window is very small, it should be difficult to trigger.
When I reviewed the code here, I suddenly realized that there
might be a problem here. Very coincidental.
Thanks.
next prev parent reply other threads:[~2021-03-23 9:18 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
2021-03-23 9:18 ` Muchun Song [this message]
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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