From 2273dea6b1e1fcdd06d207048a2cd563ed80111a Mon Sep 17 00:00:00 2001
From: Liu Shixin <liushixin2@huawei.com>
Date: Wed, 5 Mar 2025 11:54:09 +0800
Subject: [PATCH] mm/hugetlb: update nr_huge_pages and surplus_huge_pages
together
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.
Link: https://lkml.kernel.org/r/20250305035409.2391344-1-liushixin2@huawei.com
Fixes: 0c397daea1d4 ("mm, hugetlb: further simplify hugetlb allocation API")
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/hugetlb.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 438de55dd38d..af9b8c1fca67 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2259,11 +2259,20 @@ 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);
+ /*
+ * nr_huge_pages needs to be adjusted within the same lock cycle
+ * as surplus_pages, 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