From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Ashwin Chaugule <ashwinch@google.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
"Huang, Ying" <ying.huang@intel.com>,
Yang Shi <yang.shi@linux.alibaba.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH] thp: fix data loss when splitting a file pmd
Date: Wed, 11 Jul 2018 17:48:54 -0700 (PDT)
Message-ID: <alpine.LSU.2.11.1807111741430.1106@eggly.anvils> (raw)
__split_huge_pmd_locked() must check if the cleared huge pmd was dirty,
and propagate that to PageDirty: otherwise, data may be lost when a huge
tmpfs page is modified then split then reclaimed.
How has this taken so long to be noticed? Because there was no problem
when the huge page is written by a write system call (shmem_write_end()
calls set_page_dirty()), nor when the page is allocated for a write fault
(fault_dirty_shared_page() calls set_page_dirty()); but when allocated
for a read fault (which MAP_POPULATE simulates), no set_page_dirty().
Fixes: d21b9e57c74c ("thp: handle file pages in split_huge_pmd()")
Reported-by: Ashwin Chaugule <ashwinch@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: <stable@vger.kernel.org> # v4.8+
---
mm/huge_memory.c | 2 ++
1 file changed, 2 insertions(+)
--- 4.18-rc4/mm/huge_memory.c 2018-06-16 18:48:22.029173363 -0700
+++ linux/mm/huge_memory.c 2018-07-10 20:11:29.991011603 -0700
@@ -2084,6 +2084,8 @@ static void __split_huge_pmd_locked(stru
if (vma_is_dax(vma))
return;
page = pmd_page(_pmd);
+ if (!PageDirty(page) && pmd_dirty(_pmd))
+ set_page_dirty(page);
if (!PageReferenced(page) && pmd_young(_pmd))
SetPageReferenced(page);
page_remove_rmap(page, true);
next reply index
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-12 0:48 Hugh Dickins [this message]
2018-07-12 1:40 ` Yang Shi
2018-07-12 13:42 ` Kirill A. Shutemov
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