Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions

From: Jerome Glisse
Date: Sat Dec 08 2018 - 13:45:34 EST

On Sat, Dec 08, 2018 at 10:26:04AM -0800, Christoph Hellwig wrote:
> On Sat, Dec 08, 2018 at 12:47:30PM -0500, Jerome Glisse wrote:
> > Most of the user of GUP are well behave (everything under driver/gpu and
> > so is mellanox driver and many other) ie they abide by mmu notifier
> > invalidation call backs. They are a handfull of device driver that thought
> > they could just do GUP and ignore the mmu notifier part and those are the
> > one being problematic. So to me it feels like bystander are be shot for no
> > good reasons.
> get_user_pages is used by every single direct I/O, and while the race
> windows in that case are small they very much exists.

Yes and my proposal allow to fix that in even a better way than
the pin count would ie allowing to provide a callback for write
back to wait on direct I/O as you said for direct I/O it is a
small window so it would be fine to have write back wait on it.