From: David Stevens <stevensd@chromium.org>
To: linux-mm@kvack.org, Peter Xu <peterx@redhat.com>,
Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
Yang Shi <shy828301@gmail.com>,
David Hildenbrand <david@redhat.com>,
Hugh Dickins <hughd@google.com>,
linux-kernel@vger.kernel.org,
David Stevens <stevensd@chromium.org>
Subject: [PATCH 1/2] mm/khugepaged: set THP as uptodate earlier for shmem
Date: Tue, 14 Feb 2023 16:57:09 +0900 [thread overview]
Message-ID: <20230214075710.2401855-1-stevensd@google.com> (raw)
From: David Stevens <stevensd@chromium.org>
In collapse_file, mark the THP as up-to-date before inserting it into
the page cache. This fixes a race where folio_seek_hole_data would
mistake the THP for an fallocated but unwritten page. This race is
visible to userspace via data temporarily disappearing from
SEEK_DATA/SEEK_HOLE, which can cause data loss for applications that use
lseek to efficiently snapshot sparse shmem.
Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: David Stevens <stevensd@chromium.org>
---
mm/khugepaged.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 79be13133322..b648f1053d95 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1779,10 +1779,13 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
hpage->mapping = mapping;
/*
- * At this point the hpage is locked and not up-to-date.
- * It's safe to insert it into the page cache, because nobody would
- * be able to map it or use it in another way until we unlock it.
+ * Mark hpage as up-to-date before inserting it into the page cache to
+ * prevent it from being mistaken for an fallocated but unwritten page.
+ * Inserting the unfinished hpage into the page cache is safe because
+ * it is locked, so nobody can map it or use it in another way until we
+ * unlock it.
*/
+ SetPageUptodate(hpage);
xas_set(&xas, start);
for (index = start; index < end; index++) {
--
2.39.1.581.gbfd45094c4-goog
next reply other threads:[~2023-02-14 7:57 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-14 7:57 David Stevens [this message]
2023-02-14 7:57 ` [PATCH 2/2] mm/khugepaged: skip shmem with userfaultfd David Stevens
2023-02-14 22:35 ` Peter Xu
2023-02-15 1:57 ` David Stevens
2023-02-15 22:27 ` Peter Xu
2023-02-15 22:48 ` Peter Xu
2023-02-16 1:37 ` David Stevens
2023-02-16 14:41 ` Peter Xu
2023-02-16 21:58 ` Yang Shi
2023-02-16 23:07 ` Peter Xu
2023-02-16 23:52 ` Yang Shi
2023-02-17 2:00 ` David Stevens
2023-02-17 3:20 ` Yang Shi
2023-02-14 15:44 ` [PATCH 1/2] mm/khugepaged: set THP as uptodate earlier for shmem Matthew Wilcox
2023-02-15 1:33 ` David Stevens
2023-02-15 22:05 ` Peter Xu
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