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    Subject[PATCH v4 3/8] hugetlb: add per-hstate mutex to synchronize user adjustments
    Date
    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)
    --
    2.30.2
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