On 8/16/2022 10:21 AM, Haiyue Wang wrote:
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@xxxxxxxxx
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.
Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline")
Signed-off-by: Haiyue Wang <haiyue.wang@xxxxxxxxx>
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
---
Looks good to me.
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
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;
}
