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From: Miaohe Lin <linmiaohe@huawei.com>
To: Roman Gushchin <guro@fb.com>
Cc: <hannes@cmpxchg.org>, <mhocko@kernel.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: Fri, 30 Jul 2021 14:29:57 +0800	[thread overview]
Message-ID: <2a9353e0-9ece-d8d5-1387-202b01b0fdad@huawei.com> (raw)
In-Reply-To: <YQNuK+jN7pZLJTvT@carbon.lan>

On 2021/7/30 11:12, 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.
> 
> Is this a real world problem? Do I miss something?

No, this is a theoretical bug, a very race case but not impossible IMO.
Since we can't live with NULL rb_tree_per_node in soft_limit_tree, I thinks
simply continue or break here without panic is also acceptable. Or is it
more proper to choose panic here?

Thanks.

> .
> 


  reply	other threads:[~2021-07-30  6:30 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 [this message]
2021-07-30  6:44     ` Michal Hocko
2021-07-31  2:05       ` Miaohe Lin
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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