linux-kernel - [PATCH RFC v2 11/12] mm/hugetlb: Use hugetlb walker lock in page_vma_mapped

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Message-Id: <20221118011133.2179145-1-peterx@redhat.com>
Date:   Thu, 17 Nov 2022 20:11:33 -0500
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>, peterx@...hat.com,
        Nadav Amit <nadav.amit@...il.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        James Houghton <jthoughton@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...riel.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: [PATCH RFC v2 11/12] mm/hugetlb: Use hugetlb walker lock in page_vma_mapped_walk()

Hugetlb walker lock makes sure the pte_t* won't go away from under us.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 include/linux/rmap.h | 4 ++++
 mm/page_vma_mapped.c | 5 ++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 011a7530dc76..94d25a67db2b 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -13,6 +13,7 @@
 #include <linux/highmem.h>
 #include <linux/pagemap.h>
 #include <linux/memremap.h>
+#include <linux/hugetlb.h>
 
 /*
  * The anon_vma heads a list of private "related" vmas, to scan if
@@ -408,6 +409,9 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw)
 		pte_unmap(pvmw->pte);
 	if (pvmw->ptl)
 		spin_unlock(pvmw->ptl);
+	/* This needs to be after unlock of the spinlock */
+	if (is_vm_hugetlb_page(pvmw->vma))
+		hugetlb_walker_unlock();
 }
 
 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 93e13fc17d3c..5ac8a89130f6 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -169,10 +169,13 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 		if (pvmw->pte)
 			return not_found(pvmw);
 
+		hugetlb_walker_lock();
 		/* when pud is not present, pte will be NULL */
 		pvmw->pte = huge_pte_offset(mm, pvmw->address, size);
-		if (!pvmw->pte)
+		if (!pvmw->pte) {
+			hugetlb_walker_unlock();
 			return false;
+		}
 
 		pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte);
 		if (!check_pte(pvmw))
-- 
2.37.3