+ thp-fix-data-loss-when-splitting-a-file-pmd.patch added to -mm tree

The patch titled
     Subject: mm/huge_memory.c: fix data loss when splitting a file pmd
has been added to the -mm tree.  Its filename is
     thp-fix-data-loss-when-splitting-a-file-pmd.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/thp-fix-data-loss-when-splitting-a-file-pmd.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/thp-fix-data-loss-when-splitting-a-file-pmd.patch

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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: mm/huge_memory.c: fix data loss when splitting a file pmd

__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().

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1807111741430.1106@eggly.anvils
Fixes: d21b9e57c74c ("thp: handle file pages in split_huge_pmd()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Ashwin Chaugule <redacted>
Reviewed-by: Yang Shi <redacted>
Reviewed-by: Kirill A. Shutemov <redacted>
Cc: "Huang, Ying" <redacted>
Cc: <redacted>	[4.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |    2 ++
 1 file changed, 2 insertions(+)

diff -puN mm/huge_memory.c~thp-fix-data-loss-when-splitting-a-file-pmd mm/huge_memory.c

--- a/mm/huge_memory.c~thp-fix-data-loss-when-splitting-a-file-pmd
+++ a/mm/huge_memory.c

@@ -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);

_

Patches currently in -mm which might be from hughd@google.com are

thp-fix-data-loss-when-splitting-a-file-pmd.patch