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/[email protected]
Fixes: d21b9e57c74c ("thp: handle file pages in split_huge_pmd()")
Signed-off-by: Hugh Dickins <[email protected]>
Reported-by: Ashwin Chaugule <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
Reviewed-by: Kirill A. Shutemov <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: <[email protected]>	[4.8+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions