linux-kernel - Re: [PATCH v3 1/4] hugetlb: Fix wrong use of nr_online

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Message-ID: <1407c3bb-89c4-ae11-7b09-d42115ab693e@huawei.com>
Date:   Sat, 16 Apr 2022 09:21:45 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Peng Liu <liupeng256@...wei.com>, <mike.kravetz@...cle.com>,
        <david@...hat.com>, <akpm@...ux-foundation.org>,
        <yaozhenguo1@...il.com>, <baolin.wang@...ux.alibaba.com>,
        <songmuchun@...edance.com>, <liuyuntao10@...wei.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/4] hugetlb: Fix wrong use of nr_online_nodes


On 2022/4/15 13:41, Kefeng Wang wrote:
>
> On 2022/4/15 10:09, Davidlohr Bueso wrote:
>> On Wed, 13 Apr 2022, Peng Liu wrote:
>>
>>> Certain systems are designed to have sparse/discontiguous nodes. In
>>> this case, nr_online_nodes can not be used to walk through numa node.
>>> Also, a valid node may be greater than nr_online_nodes.
>>>
>>> However, in hugetlb, it is assumed that nodes are contiguous. Recheck
>>> all the places that use nr_online_nodes, and repair them one by one.
>>>
>>> Suggested-by: David Hildenbrand <david@...hat.com>
>>> Fixes: 4178158ef8ca ("hugetlbfs: fix issue of preallocation of 
>>> gigantic pages can't work")
>>> Fixes: b5389086ad7b ("hugetlbfs: extend the definition of hugepages 
>>> parameter to support node allocation")
>>> Fixes: e79ce9832316 ("hugetlbfs: fix a truncation issue in hugepages 
>>> parameter")
>>> Fixes: f9317f77a6e0 ("hugetlb: clean up potential spectre issue 
>>> warnings")
>>> Signed-off-by: Peng Liu <liupeng256@...wei.com>
>>> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>>> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
>>
>> Reviewed-by: Davidlohr Bueso <dave@...olabs.net>
>>
>> ... but
>>
>>> ---
>>> mm/hugetlb.c | 12 ++++++------
>>> 1 file changed, 6 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index b34f50156f7e..5b5a2a5a742f 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -2979,7 +2979,7 @@ int __alloc_bootmem_huge_page(struct hstate 
>>> *h, int nid)
>>>     struct huge_bootmem_page *m = NULL; /* initialize for clang */
>>>     int nr_nodes, node;
>>>
>>> -    if (nid != NUMA_NO_NODE && nid >= nr_online_nodes)
>>> +    if (nid != NUMA_NO_NODE && !node_online(nid))
>>
>> afaict null_blk could also use this, actually the whole thing wants a
>> helper - node_valid()?
>>
> This one should be unnecessary, and this patch looks has a bug,
>
> if a very nid passed to node_online(), it may crash,  could you 
> re-check it,
>
> see my changes below,
>
> 1) add tmp check against MAX_NUMNODES before node_online() check,
>
>     and move it after get tmp in hugepages_setup() , this could cover 
> both per-node alloc and normal alloc

sorry，for normal alloc, tmp is the number of huge pages, we don't  need 
the movement,   only add tmp >= MAX_NUMNODES is ok

>
> 2) due to for_each_online_node() usage, we can drop additional check 
> of nid in __alloc_bootmem_huge_page()
>