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Date:   Wed, 27 May 2020 20:20:33 -0400
From:   Jerome Glisse <>
To:, Andrew Morton <>,
        Huang Ying <>
        Steven Capper <>,
        Catalin Marinas <>,
        Rabin Vincent <>,,,
        Guo Ren <>,,
        Ralf Baechle <>,
        Paul Burton <>,
        James Hogan <>,
        Ley Foon Tan <>,,,
        Helge Deller <>,
        "James E.J. Bottomley" <>,
        Yoshinori Sato <>,
        Rich Felker <>,,
        "David S. Miller" <>,, Guan Xuetao <>,, Max Filippov <>,
        Chris Zankel <>
Subject: Cache flush issue with page_mapping_file() and swap back shmem page ?

So any arch code which uses page_mapping_file() might get the wrong
answer, this function will return NULL for a swap backed page which
can be a shmem pages. But shmem pages can still be shared among
multiple process (and possibly at different virtual addresses if
mremap was use).

Attached is a patch that changes page_mapping_file() to return the
shmem mapping for swap backed shmem page. I have not tested it (no
way for me to test all those architecture) and i spotted this while
working on something else. So i hope someone can take a closer look.


View attachment "0001-mm-fix-cache-flush-for-shmem-page-that-are-swap-back.patch" of type "text/plain" (2357 bytes)

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