Re: [PATCH 08/25] IB/uverbs: ufile must be freed only when not used anymore

[Yuval Shaia <yuval.shaia@oracle.com>]

On Thu, Jul 18, 2019 at 09:17:47AM -0300, Jason Gunthorpe wrote:
> On Thu, Jul 18, 2019 at 12:36:37AM +0300, Yuval Shaia wrote:
> > On Wed, Jul 17, 2019 at 01:45:05PM -0700, Matthew Wilcox wrote:
> > > On Wed, Jul 17, 2019 at 11:31:12PM +0300, Yuval Shaia wrote:
> > > > On Wed, Jul 17, 2019 at 04:33:13PM -0300, Jason Gunthorpe wrote:
> > > > > Like I said, drivers that require the creating ucontext as part of the
> > > > > PD and MR cannot support sharing.
> > > > 
> > > > Even if we can make sure the process that creates the MR stays alive until
> > > > all reference to this MR completes?
> > > 
> > > The kernel can't rely on userspace to do that.
> > 
> > ok, how about this: we know that for MR to be shared the memory behinds it
> > should also be shared.
> > 
> > In this case, i know it sounds horrifying but do we care that the process
> > that originally created this MR exits? i.e. how about just before the
> > process leaves this world we will find some other ucontext to hold these
> > memory mappings that driver holds?
> > Or how about moving this mapping from ucontext pointed by ib_mr directly to
> > ib_mr?
> 
> What are you worrying about? My point is we don't need to *anything*
> if the driver objects for PD and MR don't rely on the ucontext. This
> appears to be the normal case.

but we saw that mlx4 (and i think also 5) do use the ucontext, i think to
undo umem_get stuff.

> 
> MRs already work fine if they outlive the creating process.

You mean if we leave the creating process alive?

> 
> Jason