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@xxxxxxxxxx>
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@xxxxxxxxxx>
Reported-by: Ashwin Chaugule <ashwinch@xxxxxxxxxx>
Reviewed-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.8+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx are
thp-fix-data-loss-when-splitting-a-file-pmd.patch
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