Re: [PATCH 02 of 66] mm, migration: Fix race betweenshift_arg_pages and rmap_walk by guaranteeing rmap_walk finds PTEscreated within the temporary stack

[Mel Gorman]

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@xxxxxxxxxx>
> 
> 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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