linux-kernel - [PATCH v1 1/7] mm: khugepaged: retract_page_tables() use pte_offset_map

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Message-Id: <258de4356bdcc01bce0ff1f6c29b2b64a4211494.1729157502.git.zhengqi.arch@bytedance.com>
Date: Thu, 17 Oct 2024 17:47:20 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: david@...hat.com,
	hughd@...gle.com,
	willy@...radead.org,
	mgorman@...e.de,
	muchun.song@...ux.dev,
	vbabka@...nel.org,
	akpm@...ux-foundation.org,
	zokeefe@...gle.com,
	rientjes@...gle.com,
	jannh@...gle.com,
	peterx@...hat.com
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH v1 1/7] mm: khugepaged: retract_page_tables() use pte_offset_map_lock()

In retract_page_tables(), we may modify the pmd entry after acquiring the
pml and ptl, so we should also check whether the pmd entry is stable.
Using pte_offset_map_lock() to do it, and then we can also remove the
calling of the pte_lockptr().

Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
 mm/khugepaged.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 94feb85ce996c..b4f49d323c8d9 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1721,6 +1721,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
 		spinlock_t *pml;
 		spinlock_t *ptl;
 		bool skipped_uffd = false;
+		pte_t *pte;
 
 		/*
 		 * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
@@ -1757,9 +1758,15 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
 		mmu_notifier_invalidate_range_start(&range);
 
 		pml = pmd_lock(mm, pmd);
-		ptl = pte_lockptr(mm, pmd);
+		pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+		if (!pte) {
+			spin_unlock(pml);
+			mmu_notifier_invalidate_range_end(&range);
+			continue;
+		}
 		if (ptl != pml)
 			spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
+		pte_unmap(pte);
 
 		/*
 		 * Huge page lock is still held, so normally the page table
-- 
2.20.1