linux-kernel - [PATCH v4 2/9] mm: pagewalk: Take the pagetable lock in walk_pte

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Message-Id: <20191008091508.2682-3-thomas_os@shipmail.org>
Date:   Tue,  8 Oct 2019 11:15:01 +0200
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     torvalds@...ux-foundation.org,
        Thomas Hellstrom <thellstrom@...are.com>,
        Matthew Wilcox <willy@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Minchan Kim <minchan@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Huang Ying <ying.huang@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>
Subject: [PATCH v4 2/9] mm: pagewalk: Take the pagetable lock in walk_pte_range()

From: Thomas Hellstrom <thellstrom@...are.com>

Without the lock, anybody modifying a pte from within this function might
have it concurrently modified by someone else.

Cc: Matthew Wilcox <willy@...radead.org>
Cc: Will Deacon <will.deacon@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...riel.com>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Huang Ying <ying.huang@...el.com>
Cc: Jérôme Glisse <jglisse@...hat.com>
Cc: Kirill A. Shutemov <kirill@...temov.name>
Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Thomas Hellstrom <thellstrom@...are.com>
---
 mm/pagewalk.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index d48c2a986ea3..83c0b78363b4 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -10,8 +10,9 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 	pte_t *pte;
 	int err = 0;
 	const struct mm_walk_ops *ops = walk->ops;
+	spinlock_t *ptl;
 
-	pte = pte_offset_map(pmd, addr);
+	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
 	for (;;) {
 		err = ops->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
 		if (err)
@@ -22,7 +23,7 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 		pte++;
 	}
 
-	pte_unmap(pte);
+	pte_unmap_unlock(pte - 1, ptl);
 	return err;
 }
 
-- 
2.21.0