Re: [PATCH 2/2] mm,migration: Avoid race between shift_arg_pages()and rmap_walk() during migration by not migrating temporary stacks

[Christoph Lameter]

On Tue, 4 May 2010, Mel Gorman wrote:

> On Sat, May 01, 2010 at 08:56:18PM -0500, Christoph Lameter wrote:
> > On Thu, 29 Apr 2010, Mel Gorman wrote:
> >
> > > There is a race between shift_arg_pages and migration that triggers this bug.
> > > A temporary stack is setup during exec and later moved. If migration moves
> > > a page in the temporary stack and the VMA is then removed before migration
> > > completes, the migration PTE may not be found leading to a BUG when the
> > > stack is faulted.
> >
> > A simpler solution would be to not allow migration of the temporary stack?
> >
>
> The patch's intention is to not migrate pages within the temporary
> stack. What are you suggesting that is different?

A simple way to disallow migration of pages is to increment the refcount
of a page.

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