On Fri 02-08-19 11:12:44, Michal Hocko wrote:

On Thu 01-08-19 19:19:31, john.hubbard@gmail.com wrote:
[...]

quoted

2) Convert all of the call sites for get_user_pages*(), to
invoke put_user_page*(), instead of put_page(). This involves dozens of
call sites, and will take some time.

How do we make sure this is the case and it will remain the case in the
future? There must be some automagic to enforce/check that. It is simply
not manageable to do it every now and then because then 3) will simply
be never safe.

Have you considered coccinele or some other scripted way to do the
transition? I have no idea how to deal with future changes that would
break the balance though.

Yeah, that's why I've been suggesting at LSF/MM that we may need to create
a gup wrapper - say vaddr_pin_pages() - and track which sites dropping
references got converted by using this wrapper instead of gup. The
counterpart would then be more logically named as unpin_page() or whatever
instead of put_user_page().  Sure this is not completely foolproof (you can
create new callsite using vaddr_pin_pages() and then just drop refs using
put_page()) but I suppose it would be a high enough barrier for missed
conversions... Thoughts?

								Honza

-- 
Jan Kara [off-list ref]
SUSE Labs, CR