Re: [RFC PATCH v2 16/19] RDMA/uverbs: Add back pointer to system file object

Jason Gunthorpe
2019-09-11T08:20:17Z

On Wed, Sep 04, 2019 at 03:25:50PM -0700, Ira Weiny wrote:
> On Wed, Aug 14, 2019 at 09:23:08AM -0300, Jason Gunthorpe wrote:
> > On Tue, Aug 13, 2019 at 01:38:59PM -0700, Ira Weiny wrote:
> > > On Tue, Aug 13, 2019 at 03:00:22PM -0300, Jason Gunthorpe wrote:
> > > > On Tue, Aug 13, 2019 at 10:41:42AM -0700, Ira Weiny wrote:
> > > >
> > > > > And I was pretty sure uverbs_destroy_ufile_hw() would take care of (or ensure
> > > > > that some other thread is) destroying all the MR's we have associated with this
> > > > > FD.
> > > >
> > > > fd's can't be revoked, so destroy_ufile_hw() can't touch them. It
> > > > deletes any underlying HW resources, but the FD persists.
> > >
> > > I misspoke. I should have said associated with this "context". And of course
> > > uverbs_destroy_ufile_hw() does not touch the FD. What I mean is that the
> > > struct file which had file_pins hanging off of it would be getting its file
> > > pins destroyed by uverbs_destroy_ufile_hw(). Therefore we don't need the FD
> > > after uverbs_destroy_ufile_hw() is done.
> > >
> > > But since it does not block it may be that the struct file is gone before the
> > > MR is actually destroyed. Which means I think the GUP code would blow up in
> > > that case... :-(
> >
> > Oh, yes, that is true, you also can't rely on the struct file living
> > longer than the HW objects either, that isn't how the lifetime model
> > works.
>
> Reviewing all these old threads... And this made me think. While the HW
> objects may out live the struct file.
>
> They _are_ going away in a finite amount of time right? It is not like they
> could be held forever right?

Yes, at least until they become shared between FDs

Jason