linux-kernel - [PATCH RFC 03/10] mm/hugetlb: Make hugetlb_vma_maps

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Message-Id: <20221030212929.335473-4-peterx@redhat.com>
Date:   Sun, 30 Oct 2022 17:29:22 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        James Houghton <jthoughton@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, peterx@...hat.com,
        Rik van Riel <riel@...riel.com>
Subject: [PATCH RFC 03/10] mm/hugetlb: Make hugetlb_vma_maps_page() RCU-safe

RCU makes sure the pte_t* won't go away from under us.  Please refer to the
comment above huge_pte_offset() for more information.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 fs/hugetlbfs/inode.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index ac3a69fe29c3..b9e7825079c7 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -387,21 +387,26 @@ static bool hugetlb_vma_maps_page(struct vm_area_struct *vma,
 				unsigned long addr, struct page *page)
 {
 	pte_t *ptep, pte;
+	bool result = false;
+
+	/* For huge_pte_offset() */
+	rcu_read_lock();
 
 	ptep = huge_pte_offset(vma->vm_mm, addr,
 			huge_page_size(hstate_vma(vma)));
 
 	if (!ptep)
-		return false;
+		goto out;
 
 	pte = huge_ptep_get(ptep);
 	if (huge_pte_none(pte) || !pte_present(pte))
-		return false;
+		goto out;
 
 	if (pte_page(pte) == page)
-		return true;
-
-	return false;
+		result = true;
+out:
+	rcu_read_unlock();
+	return result;
 }
 
 /*
-- 
2.37.3