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.
And adjust_reservation is a boolean variable that indicates whether reservations for anonymous pages in each folio should be restored. Therefore, it should be initialized to false for each round of the loop. However, this variable is not initialized to false except when defining the current adjust_reservation variable.
This means that once adjust_reservation is set to true even once within the loop, reservations for anonymous pages will be restored unconditionally in all subsequent rounds, regardless of the folio's state.
To fix this, we need to add the missing hugetlb_lock, unlock the page_table_lock earlier so that we don't lock the hugetlb_lock inside the page_table_lock lock, and initialize adjust_reservation to false on each round within the loop.
Cc: stable@vger.kernel.org Reported-by: syzbot+417aeb05fd190f3a6da9@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=417aeb05fd190f3a6da9 Fixes: df7a6d1f6405 ("mm/hugetlb: restore the reservation if needed") Signed-off-by: Jeongjun Park aha310510@gmail.com --- v2: Fix issues with changing the page_table_lock unlock location and initializing adjust_reservation - Link to v1: https://lore.kernel.org/all/20250822055857.1142454-1-aha310510@gmail.com/ --- mm/hugetlb.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 753f99b4c718..eed59cfb5d21 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5851,7 +5851,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, spinlock_t *ptl; struct hstate *h = hstate_vma(vma); unsigned long sz = huge_page_size(h); - bool adjust_reservation = false; + bool adjust_reservation; unsigned long last_addr_mask; bool force_flush = false;
@@ -5944,6 +5944,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, sz); hugetlb_count_sub(pages_per_huge_page(h), mm); hugetlb_remove_rmap(folio); + spin_unlock(ptl);
/* * Restore the reservation for anonymous page, otherwise the @@ -5951,14 +5952,16 @@ 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. */ + adjust_reservation = false; + + spin_lock_irq(&hugetlb_lock); if (!h->surplus_huge_pages && __vma_private_lock(vma) && folio_test_anon(folio)) { folio_set_hugetlb_restore_reserve(folio); /* Reservation to be adjusted after the spin lock */ adjust_reservation = true; } - - spin_unlock(ptl); + spin_unlock_irq(&hugetlb_lock);
/* * Adjust the reservation for the region that will have the --