linux-kernel - [PATCH v3 1/3] mm: ptdump should use ptep_get

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Date:   Mon, 12 Jun 2023 16:15:43 +0100
From:   Ryan Roberts <ryan.roberts@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        SeongJae Park <sj@...nel.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Rapoport <rppt@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Uladzislau Rezki <urezki@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lorenzo Stoakes <lstoakes@...il.com>
Cc:     Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, damon@...ts.linux.dev
Subject: [PATCH v3 1/3] mm: ptdump should use ptep_get_lockless()

The page table dumper uses walk_page_range_novma() to walk the page
tables, which does not lock the PTL before calling the pte_entry()
callback. Therefore, the page table dumper's callback must use
ptep_get_lockless() rather than ptep_get() to ensure that the pte it
reads is not torn or otherwise corrupt when racing with writers.

Signed-off-by: Ryan Roberts <ryan.roberts@....com>
---
 mm/ptdump.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/ptdump.c b/mm/ptdump.c
index 8adab455a68b..03c1bdae4a43 100644
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -119,7 +119,7 @@ static int ptdump_pte_entry(pte_t *pte, unsigned long addr,
 			    unsigned long next, struct mm_walk *walk)
 {
 	struct ptdump_state *st = walk->private;
-	pte_t val = ptep_get(pte);
+	pte_t val = ptep_get_lockless(pte);
 
 	if (st->effective_prot)
 		st->effective_prot(st, 4, pte_val(val));
-- 
2.25.1