linux-kernel - Cache flush issue with page_mapping_file() and swap back shmem page ?

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Message-ID: <20200528002033.GB1992500@redhat.com>
Date:   Wed, 27 May 2020 20:20:33 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Huang Ying <ying.huang@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Steven Capper <steve.capper@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Rabin Vincent <rabinv@...s.com>,
        linux-arm-kernel@...ts.infradead.org, rmk+kernel@....linux.org.uk,
        Guo Ren <guoren@...nel.org>, linux-mips@...r.kernel.org,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paulburton@...nel.org>,
        James Hogan <jhogan@...nel.org>,
        Ley Foon Tan <lftan@...era.com>,
        nios2-dev@...ts.rocketboards.org, linux-parisc@...r.kernel.org,
        Helge Deller <deller@....de>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        sparclinux@...r.kernel.org, Guan Xuetao <gxt@....edu.cn>,
        linux-xtensa@...ux-xtensa.org, Max Filippov <jcmvbkbc@...il.com>,
        Chris Zankel <chris@...kel.net>
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.

Cheers,
Jérôme

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