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From:   Peter Xu <peterx@redhat.com>
To:     linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        James Houghton <jthoughton@google.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        David Hildenbrand <david@redhat.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Mike Kravetz <mike.kravetz@oracle.com>, peterx@redhat.com,
        Rik van Riel <riel@surriel.com>
Subject: [PATCH RFC 05/10] mm/hugetlb: Make walk_hugetlb_range() RCU-safe
Date:   Sun, 30 Oct 2022 17:29:24 -0400
Message-Id: <20221030212929.335473-6-peterx@redhat.com>
In-Reply-To: <20221030212929.335473-1-peterx@redhat.com>
References: <20221030212929.335473-1-peterx@redhat.com>
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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@redhat.com>
---
 mm/pagewalk.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 7f1c9b274906..bbc71c750576 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -302,6 +302,9 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end,
 	const struct mm_walk_ops *ops = walk->ops;
 	int err = 0;
 
+	/* For huge_pte_offset() */
+	rcu_read_lock();
+
 	do {
 		next = hugetlb_entry_end(h, addr, end);
 		pte = huge_pte_offset(walk->mm, addr & hmask, sz);
@@ -315,6 +318,8 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end,
 			break;
 	} while (addr = next, addr != end);
 
+	rcu_read_unlock();
+
 	return err;
 }
 
-- 
2.37.3