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    SubjectRe: [PATCH 02 of 66] mm, migration: Fix race between shift_arg_pages and rmap_walk by guaranteeing rmap_walk finds PTEs created within the temporary stack
    On Thu, Nov 18, 2010 at 11:13:49AM +0000, Mel Gorman wrote:
    > > This patch fixes the problem by using two VMAs - one which covers the temporary
    > > stack and the other which covers the new location. This guarantees that rmap
    > > can always find the migration PTE even if it is copied while rmap_walk is
    > > taking place.
    > >
    > > Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
    >
    > This old chestnut. IIRC, this was the more complete solution to a fix that made
    > it into mainline. The patch still looks reasonable. It does add a kmalloc()
    > but I can't remember if we decided we were ok with it or not. Can you remind
    > me? More importantly, it appears to be surviving the original testcase that
    > this bug was about (20 minutes so far but will leave it a few hours). Assuming
    > the test does not crash;
    >

    Incidentally, after 6.5 hours this still hasn't crashed. Previously a
    worst case reproduction scenario for the bug was around 35 minutes.

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab


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