I was looking at the stack expansion code, and I'm not convinced it's safe. Aside from the obvious scariness of down_read(&mmap_sem) not actually preventing vma changes, I think there's a real race. Suppose that you have a VM_GROWSDOWN vma above a VM_GROWSUP vma with a single-page gap between them. Suppose further that they have different anon_vma roots. If one ends up in expand_downwards and the other ends up in expand_upwards at the same time, then each one can take page_table_lock without re-checking that there's still room to expand. The result will be two vmas that share a page. (This is presumably only possible on ia64.) --Andy -- 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>