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

[Peter Xu]

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@xxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
 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