Re: [GIT PULL] please pull ummunotify

Brice Goglin
2009-09-11T06:15:19Z

Roland Dreier wrote:
> > Can I this version already solved fork() + COW issue? if so, could you
> > please explain what happen at fork. Obviously RDMA point to either parent
> > or child page, not both. but Corrent COW rule is, first touch process
> > get copyed page and other process still own original page. I think it's
> > unpecected behavior form RDMA.
>
> No, ummunotify doesn't really help that much with fork() + COW. If a
> parent forks and then touches pages that are actively in use for RDMA,
> then of course they get COWed and RDMA goes to the wrong memory (from
> the point of view of the parent).
>

My understanding of the code is that fork will end-up calling
copy_page_range() on all VMA, and copy_page_range() calls
mmu_notifier_invalidate_range_start() if is_cow_mapping() is true,
which should be the case here. So you should get some invalidate events
on fork.

Brice