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From:   Peter Xu <peterx@redhat.com>
To:     linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc:     David Hildenbrand <david@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Rik van Riel <riel@surriel.com>, peterx@redhat.com,
        Miaohe Lin <linmiaohe@huawei.com>,
        Jann Horn <jannh@google.com>,
        James Houghton <jthoughton@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: [PATCH v4 6/9] mm/hugetlb: Make hugetlb_follow_page_mask() safe to pmd unshare
Date:   Fri, 16 Dec 2022 10:52:19 -0500
Message-Id: <20221216155219.2043714-1-peterx@redhat.com>
In-Reply-To: <20221216155100.2043537-1-peterx@redhat.com>
References: <20221216155100.2043537-1-peterx@redhat.com>
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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>
Reviewed-by: John Hubbard <jhubbard@nvidia.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 64512a151567..0bf0abea388d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6375,9 +6375,10 @@ 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);
@@ -6400,6 +6401,8 @@ 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