From: Shakeel Butt <shakeelb@google.com>
To: Yang Shi <yang.shi@linux.alibaba.com>,
Kirill Tkhai <ktkhai@virtuozzo.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Hugh Dickins <hughd@google.com>, Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>
Cc: Qian Cai <cai@lca.pw>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: list corruption in deferred_split_scan()
Date: Tue, 16 Jul 2019 16:36:18 -0700 [thread overview]
Message-ID: <CALvZod7+ComCUROSBaj==r0VmCczs=npP4u6C9LuJWNWdfB0Pg@mail.gmail.com> (raw)
In-Reply-To: <e5aa1f5b-b955-5b8e-f502-7ac5deb141a7@linux.alibaba.com>
Adding related people.
The thread starts at:
http://lkml.kernel.org/r/1562795006.8510.19.camel@lca.pw
On Mon, Jul 15, 2019 at 8:01 PM Yang Shi <yang.shi@linux.alibaba.com> wrote:
>
>
>
> On 7/15/19 6:36 PM, Qian Cai wrote:
> >
> >> On Jul 15, 2019, at 8:22 PM, Yang Shi <yang.shi@linux.alibaba.com> wrote:
> >>
> >>
> >>
> >> On 7/15/19 2:23 PM, Qian Cai wrote:
> >>> On Fri, 2019-07-12 at 12:12 -0700, Yang Shi wrote:
> >>>>> Another possible lead is that without reverting the those commits below,
> >>>>> kdump
> >>>>> kernel would always also crash in shrink_slab_memcg() at this line,
> >>>>>
> >>>>> map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map, true);
> >>>> This looks a little bit weird. It seems nodeinfo[nid] is NULL? I didn't
> >>>> think of where nodeinfo was freed but memcg was still online. Maybe a
> >>>> check is needed:
> >>> Actually, "memcg" is NULL.
> >> It sounds weird. shrink_slab() is called in mem_cgroup_iter which does pin the memcg. So, the memcg should not go away.
> > Well, the commit “mm: shrinker: make shrinker not depend on memcg kmem” changed this line in shrink_slab_memcg(),
> >
> > - if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg))
> > + if (!mem_cgroup_online(memcg))
> > return 0;
> >
> > Since the kdump kernel has the parameter “cgroup_disable=memory”, shrink_slab_memcg() will no longer be able to handle NULL memcg from mem_cgroup_iter() as,
> >
> > if (mem_cgroup_disabled())
> > return NULL;
>
> Aha, yes. memcg_kmem_enabled() implicitly checks !mem_cgroup_disabled().
> Thanks for figuring this out. I think we need add mem_cgroup_dsiabled()
> check before calling shrink_slab_memcg() as below:
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a0301ed..2f03c61 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -701,7 +701,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int
> nid,
> unsigned long ret, freed = 0;
> struct shrinker *shrinker;
>
> - if (!mem_cgroup_is_root(memcg))
> + if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
> return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
>
> if (!down_read_trylock(&shrinker_rwsem))
>
We were seeing unneeded oom-kills on kernels with
"cgroup_disabled=memory" and Yang's patch series basically expose the
bug to crash. I think the commit aeed1d325d42 ("mm/vmscan.c:
generalize shrink_slab() calls in shrink_node()") missed the case for
"cgroup_disabled=memory". However I am surprised that root_mem_cgroup
is allocated even for "cgroup_disabled=memory" and it seems like
css_alloc() is called even before checking if the corresponding
controller is disabled.
Yang, can you please send the above change with signed-off and CC to
stable as well?
thanks,
Shakeel
next prev parent reply other threads:[~2019-07-16 23:36 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-10 21:43 list corruption in deferred_split_scan() Qian Cai
2019-07-11 0:16 ` Yang Shi
2019-07-11 21:07 ` Qian Cai
2019-07-12 19:12 ` Yang Shi
2019-07-13 4:41 ` Yang Shi
2019-07-15 21:23 ` Qian Cai
2019-07-16 0:22 ` Yang Shi
2019-07-16 1:36 ` Qian Cai
2019-07-16 3:00 ` Yang Shi
2019-07-16 23:36 ` Shakeel Butt [this message]
2019-07-17 0:12 ` Yang Shi
2019-07-17 17:02 ` Shakeel Butt
2019-07-17 17:09 ` Yang Shi
2019-07-19 0:54 ` Qian Cai
2019-07-19 0:59 ` Yang Shi
2019-07-24 18:10 ` Qian Cai
2019-07-15 4:52 ` Yang Shi
2019-07-24 21:13 ` Qian Cai
2019-07-25 21:46 ` Yang Shi
2019-08-05 22:15 ` Yang Shi
2019-08-06 1:05 ` Qian Cai
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