Re: [PATCH v3 1/9] mm: add overflow and underflow checks for page->_refcount

[Pasha Tatashin <pasha.tatashin@soleen.com>]

> > This is not only about chasing a bug. This also about preventing
> > memory corruption and information leaking that are caused by ref_count
> > bugs from happening.
>
> So you mean it like a security hardening feature, not just debugging? To me
> it's dubious to put security hardening under CONFIG_DEBUG_VM. I think it's
> just Fedora that uses DEBUG_VM in general production kernels?

In our (Google) internal kernel, I added another macro:
PAGE_REF_BUG(cond, page) to replace VM_BUG_ON_PAGE() in page_ref.h.
The new macro keeps the asserts always enabled.  I was thinking of
adding something like this to the upstream kernel as well, however, I
am worried about performance implications of having extra conditions
in these routines, so I think we would need yet another config which
decouples DEBUG_VM and some security crucial VM asserts. However, to
reduce controversial discussions, I decided not to do this as part of
this series, and perhaps do it as a follow-up work.

Pasha