Re: mmu_notifier: Move mmu_notifier_release up to get rid of the invalidat_all() callback

[Andrea Arcangeli <andrea@qumranet.com>]

On Thu, Jan 31, 2008 at 02:21:58PM -0800, Christoph Lameter wrote:
> Is this okay for KVM too?

->release isn't implemented at all in KVM, only the list_del generates
complications.

I think current code could be already safe through the mm_count pin,
becasue KVM relies on the fact anybody pinning through mm_count like
KVM does, is forbidden to call unregister and it's forced to wait the
auto-disarming when mm_users hits zero, but I feel like something's
still wrong if I think that I'm not using call_rcu to free the
notifier (OTOH we agreed the list had to be frozen and w/o readers
(modulo _release) before _release is called, so if this initial
assumption is ok it seems I may be safe w/o call_rcu?).

But it's really tricky path. Anyway this is the last of my worries
right now, it works perfectly fine with a single user obviously, and
the moment KVM threads runs remotely through GRU/XPMEM isn't happening
too soon ;) so let's concentrate on the rest first. I can say
hlist_del_init doesn't seem to provide any benefit given nobody could
possibly decide to call register or unregister after _release run.