In alloc_surplus_hugetlb_folio(), we increase nr_huge_pages and
surplus_huge_pages separately. In the middle window, if we set
nr_hugepages to smaller and satisfy count < persistent_huge_pages(h),
the surplus_huge_pages will be increased by adjust_pool_surplus().
After adding delay in the middle window, we can reproduce the problem
easily by following step:
1. echo 3 > /proc/sys/vm/nr_overcommit_hugepages
2. mmap two hugepages. When nr_huge_pages=2 and surplus_huge_pages=1,
goto step 3.
3. echo 0 > /proc/sys/vm/nr_huge_pages
Finally, nr_huge_pages is less than surplus_huge_pages.
To fix the problem, call only_alloc_fresh_hugetlb_folio() instead and
move down __prep_account_new_huge_page() into the hugetlb_lock.
Fixes: 0c397daea1d4 ("mm, hugetlb: further simplify hugetlb allocation API")
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
---
mm/hugetlb.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 9faa1034704ff..0b02ea1c39e63 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2253,11 +2253,19 @@ static struct folio *alloc_surplus_hugetlb_folio(struct hstate *h,
goto out_unlock;
spin_unlock_irq(&hugetlb_lock);
- folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask);
+ folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, NULL);
if (!folio)
return NULL;
+ hugetlb_vmemmap_optimize_folio(h, folio);
+
spin_lock_irq(&hugetlb_lock);
+ /*
+ * Update nr_huge_pages and surplus_huge_pages together,
+ * otherwise it might confuse persistent_huge_pages() momentarily.
+ */
+ __prep_account_new_huge_page(h, nid);
+
/*
* We could have raced with the pool size change.
* Double check that and simply deallocate the new page
--
2.34.1
