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Subject: Re: [PATCH v4 3/8] hugetlb: add per-hstate mutex to synchronize user
 adjustments
To:     Mike Kravetz <mike.kravetz@oracle.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Cc:     Roman Gushchin <guro@fb.com>, Michal Hocko <mhocko@suse.com>,
        Shakeel Butt <shakeelb@google.com>,
        Oscar Salvador <osalvador@suse.de>,
        Muchun Song <songmuchun@bytedance.com>,
        David Rientjes <rientjes@google.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Matthew Wilcox <willy@infradead.org>,
        HORIGUCHI NAOYA <naoya.horiguchi@nec.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        Waiman Long <longman@redhat.com>, Peter Xu <peterx@redhat.com>,
        Mina Almasry <almasrymina@google.com>,
        Hillf Danton <hdanton@sina.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Barry Song <song.bao.hua@hisilicon.com>,
        Will Deacon <will@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20210405230043.182734-1-mike.kravetz@oracle.com>
 <20210405230043.182734-4-mike.kravetz@oracle.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <ee2a4ec1-9a44-5870-fb66-f48a14a518e8@redhat.com>
Date:   Wed, 7 Apr 2021 11:28:17 +0200
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On 06.04.21 01:00, Mike Kravetz wrote:
> The helper routine hstate_next_node_to_alloc accesses and modifies the
> hstate variable next_nid_to_alloc.  The helper is used by the routines
> alloc_pool_huge_page and adjust_pool_surplus.  adjust_pool_surplus is
> called with hugetlb_lock held.  However, alloc_pool_huge_page can not
> be called with the hugetlb lock held as it will call the page allocator.
> Two instances of alloc_pool_huge_page could be run in parallel or
> alloc_pool_huge_page could run in parallel with adjust_pool_surplus
> which may result in the variable next_nid_to_alloc becoming invalid
> for the caller and pages being allocated on the wrong node.
> 
> Both alloc_pool_huge_page and adjust_pool_surplus are only called from
> the routine set_max_huge_pages after boot.  set_max_huge_pages is only
> called as the reusult of a user writing to the proc/sysfs nr_hugepages,
> or nr_hugepages_mempolicy file to adjust the number of hugetlb pages.
> 
> It makes little sense to allow multiple adjustment to the number of
> hugetlb pages in parallel.  Add a mutex to the hstate and use it to only
> allow one hugetlb page adjustment at a time.  This will synchronize
> modifications to the next_nid_to_alloc variable.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> ---
>   include/linux/hugetlb.h | 1 +
>   mm/hugetlb.c            | 8 ++++++++
>   2 files changed, 9 insertions(+)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index d9b78e82652f..b92f25ccef58 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -566,6 +566,7 @@ HPAGEFLAG(Freed, freed)
>   #define HSTATE_NAME_LEN 32
>   /* Defines one hugetlb page size */
>   struct hstate {
> +	struct mutex resize_lock;
>   	int next_nid_to_alloc;
>   	int next_nid_to_free;
>   	unsigned int order;
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1d62f0492e7b..8497a3598c86 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2730,6 +2730,11 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>   	else
>   		return -ENOMEM;
>   
> +	/*
> +	 * resize_lock mutex prevents concurrent adjustments to number of
> +	 * pages in hstate via the proc/sysfs interfaces.
> +	 */
> +	mutex_lock(&h->resize_lock);
>   	spin_lock(&hugetlb_lock);
>   
>   	/*
> @@ -2762,6 +2767,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>   	if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) {
>   		if (count > persistent_huge_pages(h)) {
>   			spin_unlock(&hugetlb_lock);
> +			mutex_unlock(&h->resize_lock);
>   			NODEMASK_FREE(node_alloc_noretry);
>   			return -EINVAL;
>   		}
> @@ -2836,6 +2842,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>   out:
>   	h->max_huge_pages = persistent_huge_pages(h);
>   	spin_unlock(&hugetlb_lock);
> +	mutex_unlock(&h->resize_lock);
>   
>   	NODEMASK_FREE(node_alloc_noretry);
>   
> @@ -3323,6 +3330,7 @@ void __init hugetlb_add_hstate(unsigned int order)
>   	BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE);
>   	BUG_ON(order == 0);
>   	h = &hstates[hugetlb_max_hstate++];
> +	mutex_init(&h->resize_lock);
>   	h->order = order;
>   	h->mask = ~(huge_page_size(h) - 1);
>   	for (i = 0; i < MAX_NUMNODES; ++i)
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb