On Tue, Dec 24, 2013 at 03:07:05PM +0900, Joonsoo Kim wrote: > On Mon, Dec 23, 2013 at 10:01:10PM -0500, Sasha Levin wrote: > > On 12/23/2013 09:51 PM, Joonsoo Kim wrote: > > >On Mon, Dec 23, 2013 at 12:24:02PM -0500, Sasha Levin wrote: > > >>>Ping? > > >>> > > >>>I've also Cc'ed the "this page shouldn't be locked at all" team. > > >Hello, > > > > > >I can't find the reason of this problem. > > >If it is reproducible, how about bisecting? > > > > While it reproduces under fuzzing it's pretty hard to bisect it with > > the amount of issues uncovered by trinity recently. > > > > I can add any debug code to the site of the BUG if that helps. > > Good! > It will be helpful to add dump_page() in migration_entry_to_page(). > > Thanks. > Minchan teaches me that there is possible race condition between fork and migration. Please consider following situation. Process A (do migration) Process B (parents) Process C (child) try_to_unmap() for migration <begin> fork setup migration entry to B's vma ... try_to_unmap() for migration <end> move_to_new_page() link new vma into interval tree remove_migration_ptes() <begin> check and clear migration entry on C's vma ... copy_one_pte: ... now, B and C have migration entry ... ... check and clear migration entry on B's vma ... ... remove_migration_ptes() <end> Eventually, migration entry on C's vma is left. And then, when C exits, above BUG_ON() can be triggered. I'm not sure the I am right, so please think of it together. :) And I'm not sure again that above assumption is related to this trigger report, since this may exist for a long time. So my question to mm folks is is above assumption possible and do we have any protection mechanism on this race? Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>