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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
