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

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Date:   Tue, 19 Apr 2022 16:54:02 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Peng Liu <liupeng256@...wei.com>, <mike.kravetz@...cle.com>,
        <david@...hat.com>, <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 2022/4/19 12:40, Andrew Morton wrote:
> On Sat, 16 Apr 2022 09:21:45 +0800 Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
>
>> 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
>>
> Does the v4 patch address the issues which were raised in this thread?
Yes， v4 has fix this.
>
>
> --- a/mm/hugetlb.c~hugetlb-fix-wrong-use-of-nr_online_nodes-v4
> +++ a/mm/hugetlb.c
> @@ -2986,8 +2986,6 @@ int __alloc_bootmem_huge_page(struct hst
>   	struct huge_bootmem_page *m = NULL; /* initialize for clang */
>   	int nr_nodes, node;
>   
> -	if (nid != NUMA_NO_NODE && !node_online(nid))
> -		return 0;
>   	/* do node specific alloc */
>   	if (nid != NUMA_NO_NODE) {
>   		m = memblock_alloc_try_nid_raw(huge_page_size(h), huge_page_size(h),
> @@ -4174,7 +4172,7 @@ static int __init hugepages_setup(char *
>   				pr_warn("HugeTLB: architecture can't support node specific alloc, ignoring!\n");
>   				return 0;
>   			}
> -			if (!node_online(tmp))
> +			if (tmp >= MAX_NUMNODES || !node_online(tmp))
>   				goto invalid;
>   			node = array_index_nospec(tmp, MAX_NUMNODES);
>   			p += count + 1;
> _
>
> .