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    Subject[PATCH v1] mm: migration: fix the FOLL_GET failure on following huge page
    Date
    Not all huge page APIs support FOLL_GET option, so the __NR_move_pages
    will fail to get the page node information for huge page.

    This is an temporary solution to mitigate the racing fix.

    After supporting follow huge page by FOLL_GET is done, this fix can be
    reverted safely.

    Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline")
    Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
    ---
    mm/migrate.c | 10 ++++++++--
    1 file changed, 8 insertions(+), 2 deletions(-)

    diff --git a/mm/migrate.c b/mm/migrate.c
    index 6a1597c92261..581dfaad9257 100644
    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -1848,6 +1848,7 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,

    for (i = 0; i < nr_pages; i++) {
    unsigned long addr = (unsigned long)(*pages);
    + unsigned int foll_flags = FOLL_DUMP;
    struct vm_area_struct *vma;
    struct page *page;
    int err = -EFAULT;
    @@ -1856,8 +1857,12 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
    if (!vma)
    goto set_status;

    + /* Not all huge page follow APIs support 'FOLL_GET' */
    + if (!is_vm_hugetlb_page(vma))
    + foll_flags |= FOLL_GET;
    +
    /* FOLL_DUMP to ignore special (like zero) pages */
    - page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
    + page = follow_page(vma, addr, foll_flags);

    err = PTR_ERR(page);
    if (IS_ERR(page))
    @@ -1865,7 +1870,8 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,

    if (page && !is_zone_device_page(page)) {
    err = page_to_nid(page);
    - put_page(page);
    + if (foll_flags & FOLL_GET)
    + put_page(page);
    } else {
    err = -ENOENT;
    }
    --
    2.37.1
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