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    SubjectRe: [patch] cache flush bug in mm/filemap.c (all kernels >= 2.5.30(at least))
    On Sun, May 25, 2003 at 08:19:32PM -0700, David S. Miller wrote:
    > Oh yes, this part is. If you don't ensure this, everything
    > breaks.
    >
    > At the end of an I/O operation, say to a page cache page, that
    > data ought to be visible equally to a userspace vs. a kernel
    > space mapping to that page.
    >
    > For example, this is why we use language about "cpu visibility" in the
    > DMA api documentation and not "kernel cpu visibility" :-) And because
    > PIO transfers are basically pseudo-DMA they need to make the same exact
    > guarentees.
    >
    > If you've been living in a world where you didn't think this is
    > necessary, I certainly feel bad for you :-)

    Ok, so the flush_dcache_page() interface looses this; the original
    placement of the flush_page_to_ram() ensured that data written by
    device drivers was visible to user space.

    Maybe the BIO layer can handle this - the same problem exists when
    (and if) BIO uses a bounce buffer, so it would have to be handled
    there. Jens?

    Lothar - can you confirm that your problem vanishes when you turn off
    write allocation on the caches please? (cachepolicy=writeback)

    --
    Russell King (rmk@arm.linux.org.uk) The developer of ARM Linux
    http://www.arm.linux.org.uk/personal/aboutme.html

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