[PATCH] mm/hugetlb: add missing hugetlb_lock in __unmap_hugepage_range()

[Jeongjun Park]

When restoring a reservation for an anonymous page, we need to check to
freeing a surplus. However, __unmap_hugepage_range() causes data race
because it reads h->surplus_huge_pages without the protection of
hugetlb_lock.

Therefore, we need to add missing hugetlb_lock.

Reported-by: syzbot+417aeb05fd190f3a6da9@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=417aeb05fd190f3a6da9
Fixes: df7a6d1f6405 ("mm/hugetlb: restore the reservation if needed")
Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
---
 mm/hugetlb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 753f99b4c718..e8d95a314df2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5951,6 +5951,8 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		 * If there we are freeing a surplus, do not set the restore
 		 * reservation bit.
 		 */
+		spin_lock_irq(&hugetlb_lock);
+
 		if (!h->surplus_huge_pages && __vma_private_lock(vma) &&
 		    folio_test_anon(folio)) {
 			folio_set_hugetlb_restore_reserve(folio);
@@ -5958,6 +5960,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
 			adjust_reservation = true;
 		}
 
+		spin_unlock_irq(&hugetlb_lock);
 		spin_unlock(ptl);
 
 		/*
--