Re: [PATCH 1/6] mmput: use notifier chain to call subsystem exit handler.

[Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>]

On Tue, Jul 01, 2014 at 03:33:44PM -0400, Jerome Glisse wrote:
> On Tue, Jul 01, 2014 at 01:00:18PM +0200, Joerg Roedel wrote:
> > No, its not in this case. The file descriptor is used to connect a
> > process address space with a device context. Thus without the mappings
> > the file-descriptor is useless and the mappings should stay in-tact
> > until the fd is closed.
> > 
> > It would be a very bad semantic for userspace if a fd that is passed on
> > fails on the other side because the sending process died.
> 
> Consider use case where there is no file associated with the mmu_notifier
> ie there is no device file descriptor that could hold and take care of
> mmu_notifier destruction and cleanup. We need this call chain for this
> case.

Example of such a use-case where no fd will be associated?

Anyway, even without an fd, there will always be something that sets the
mm->device binding up (calling mmu_notifier_register) and tears it down
in the end (calling mmu_notifier_unregister). And this will be the
places where any resources left from the .release call-back can be
cleaned up.


	Joerg