On Mon, May 10, 2010 at 12:41:07PM -0500, Christoph Lameter wrote: > 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. > I guess it could be done by walking the page-tables in advance of the move and elevating the page count of any pages faulted and then finding those pages afterwards. The fail path would be a bit of a pain though if the page tables are partially moved though. It's unnecessarily complicated when the temporary stack can be easily avoided. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>