[PATCH v2 06/10] mm/hugetlb: Make hugetlb_follow_page_mask() safe to pmd unshare

Peter Xu
2022-12-07T20:32:10Z

Since hugetlb_follow_page_mask() walks the pgtable, it needs the vma lock
to make sure the pgtable page will not be freed concurrently.

Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/hugetlb.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 49f73677a418..3fbbd599d015 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6226,9 +6226,10 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
if (WARN_ON_ONCE(flags & FOLL_PIN))
return NULL;

+ hugetlb_vma_lock_read(vma);
pte = huge_pte_offset(mm, haddr, huge_page_size(h));
if (!pte)
- return NULL;
+ goto out_unlock;

ptl = huge_pte_lock(h, mm, pte);
entry = huge_ptep_get(pte);
@@ -6251,6 +6252,8 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
}
out:
spin_unlock(ptl);
+out_unlock:
+ hugetlb_vma_unlock_read(vma);
return page;
}

--
2.37.3