mm: migration: fix the FOLL_GET failure on following huge page

Not all huge page APIs support FOLL_GET option, so move_pages() syscall
will fail to get the page node information for some huge pages.

Like x86 on linux 5.19 with 1GB huge page API follow_huge_pud(), it will
return NULL page for FOLL_GET when calling move_pages() syscall with the
NULL 'nodes' parameter, the 'status' parameter has '-2' error in array.

Note: follow_huge_pud() now supports FOLL_GET in linux 6.0.
Link: https://lore.kernel.org/all/20220714042420.1847125-3-naoya.horiguchi@linux.dev
But these huge page APIs don't support FOLL_GET:
  1. follow_huge_pud() in arch/s390/mm/hugetlbpage.c
  2. follow_huge_addr() in arch/ia64/mm/hugetlbpage.c
     It will cause WARN_ON_ONCE for FOLL_GET.
  3. follow_huge_pgd() in mm/hugetlb.c

This is an temporary solution to mitigate the side effect of the race
condition fix by calling follow_page() with FOLL_GET set for huge pages.

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

Link: https://lkml.kernel.org/r/20220823135841.934465-2-haiyue.wang@intel.com
Link: https://lkml.kernel.org/r/20220812084921.409142-1-haiyue.wang@intel.com
Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline")
Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 6a1597c..581dfaa 100644 (file)
--- 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;
                }