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From: Miaohe Lin <linmiaohe@huawei.com>
To: Michal Hocko <mhocko@suse.com>, Roman Gushchin <guro@fb.com>
Cc: <hannes@cmpxchg.org>, <vdavydov.dev@gmail.com>,
	<akpm@linux-foundation.org>, <shakeelb@google.com>,
	<willy@infradead.org>, <alexs@kernel.org>,
	<richard.weiyang@gmail.com>, <songmuchun@bytedance.com>,
	<linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
	<cgroups@vger.kernel.org>
Subject: Re: [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup_init()
Date: Sat, 31 Jul 2021 10:05:51 +0800	[thread overview]
Message-ID: <f7a22702-cd08-6b15-48c7-68523c38060b@huawei.com> (raw)
In-Reply-To: <YQOf0TKOXpGRQFHF@dhcp22.suse.cz>

On 2021/7/30 14:44, Michal Hocko wrote:
> On Thu 29-07-21 20:12:43, Roman Gushchin wrote:
>> On Thu, Jul 29, 2021 at 08:57:54PM +0800, Miaohe Lin wrote:
>>> rtpn might be NULL in very rare case. We have better to check it before
>>> dereferencing it. Since memcg can live with NULL rb_tree_per_node in
>>> soft_limit_tree, warn this case and continue.
>>>
>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>> ---
>>>  mm/memcontrol.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>>> index 5b4592d1e0f2..70a32174e7c4 100644
>>> --- a/mm/memcontrol.c
>>> +++ b/mm/memcontrol.c
>>> @@ -7109,6 +7109,8 @@ static int __init mem_cgroup_init(void)
>>>  		rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL,
>>>  				    node_online(node) ? node : NUMA_NO_NODE);
>>>  
>>> +		if (WARN_ON_ONCE(!rtpn))
>>> +			continue;
>>
>> I also really doubt that it makes any sense to continue in this case.
>> If this allocations fails (at the very beginning of the system's life, it's an __init function),
>> something is terribly wrong and panic'ing on a NULL-pointer dereference sounds like
>> a perfect choice.
> 
> Moreover this is 24B allocation during early boot. Kernel will OOM and
> panic when not being able to find any victim. I do not think we need to

Agree with you. But IMO it may not be a good idea to leave the rtpn without NULL check. We should defend
it though it could hardly happen. But I'm not insist on this check. I will drop this patch if you insist.

Thanks both of you.

> do any special handling here.
> 


  reply	other threads:[~2021-07-31  2:07 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-29 12:57 [PATCH 0/5] Cleanups and fixup for memcontrol Miaohe Lin
2021-07-29 12:57 ` [PATCH 1/5] mm, memcg: remove unused functions Miaohe Lin
2021-07-29 14:07   ` Shakeel Butt
2021-07-29 14:07     ` Shakeel Butt
2021-07-30  2:39   ` Muchun Song
2021-07-30  2:39     ` Muchun Song
2021-07-30  2:57   ` Roman Gushchin
2021-07-30  6:45   ` Michal Hocko
2021-07-29 12:57 ` [PATCH 2/5] mm, memcg: narrow the scope of percpu_charge_mutex Miaohe Lin
2021-07-30  2:42   ` Muchun Song
2021-07-30  2:42     ` Muchun Song
2021-07-30  3:06   ` Roman Gushchin
2021-07-30  6:50     ` Michal Hocko
2021-07-31  2:29       ` Miaohe Lin
2021-08-02  6:49         ` Michal Hocko
2021-08-02  9:54           ` Miaohe Lin
2021-08-03  3:40         ` Roman Gushchin
2021-08-03  6:29           ` Miaohe Lin
2021-08-03  7:11             ` Michal Hocko
2021-08-03  7:13               ` Roman Gushchin
2021-08-03  7:27                 ` Michal Hocko
2021-08-03  9:33             ` Muchun Song
2021-08-03  9:33               ` Muchun Song
2021-08-03 10:50               ` Miaohe Lin
2021-08-03 14:15       ` Johannes Weiner
2021-08-04  8:20         ` Michal Hocko
2021-08-05  1:44           ` Miaohe Lin
2021-07-30  6:46   ` Michal Hocko
2021-07-29 12:57 ` [PATCH 3/5] mm, memcg: save some atomic ops when flush is already true Miaohe Lin
2021-07-29 14:40   ` Shakeel Butt
2021-07-29 14:40     ` Shakeel Butt
2021-07-30  2:37   ` Muchun Song
2021-07-30  2:37     ` Muchun Song
2021-07-30  3:07   ` Roman Gushchin
2021-07-30  6:51   ` Michal Hocko
2021-07-29 12:57 ` [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup_init() Miaohe Lin
2021-07-29 13:52   ` Matthew Wilcox
2021-07-30  1:50     ` Miaohe Lin
2021-07-30  3:12   ` Roman Gushchin
2021-07-30  6:29     ` Miaohe Lin
2021-07-30  6:44     ` Michal Hocko
2021-07-31  2:05       ` Miaohe Lin [this message]
2021-08-02  6:43         ` Michal Hocko
2021-08-02 10:00           ` Miaohe Lin
2021-08-02 10:42             ` Michal Hocko
2021-08-02 11:18               ` Miaohe Lin
2021-07-29 12:57 ` [PATCH 5/5] mm, memcg: always call __mod_node_page_state() with preempt disabled Miaohe Lin
2021-07-29 14:39   ` Shakeel Butt
2021-07-29 14:39     ` Shakeel Butt
2021-07-30  1:52     ` Miaohe Lin
2021-07-30  2:33       ` [External] " Muchun Song
2021-07-30  2:33         ` Muchun Song
2021-07-30  2:46         ` Miaohe Lin

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