Re: [External] [PATCH v2 3/8] hugetlb: add per-hstate mutex to synchronize user adjustments

[Muchun Song]

On Tue, Mar 30, 2021 at 7:24 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> 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@xxxxxxxxxx>

Thanks Mike.

Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>

> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
>  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)
> --
> 2.30.2
>