Re: [PATCH 3/3] drm/i915: Ignore duplicate VMA stored within the per-object handle LUT

Joonas Lahtinen
2017-09-18T13:56:34Z

On Wed, 2017-08-30 at 12:56 +0100, Chris Wilson wrote:
> Quoting Joonas Lahtinen (2017-08-30 12:07:47)
> > On Wed, 2017-08-23 at 11:20 +0100, Chris Wilson wrote:
> > > Quoting Joonas Lahtinen (2017-08-23 11:05:18)
> > > > On Tue, 2017-08-22 at 12:05 +0100, Chris Wilson wrote:
> > > > > By using drm_gem_flink/drm_gem_open on an object using the same fd, it
> > > > > is possible for a client to create multiple handles pointing to the same
> > > > > object (tied to the same contexts and VMA), as exemplified by
> > > > > igt::gem_handle_to_libdrm_bo(). Since this duplication has been possible
> > > > > since forever, we cannot assume that the handle:(fpriv, object) is
> > > > > unique and so must handle the multiple users of a single VMA.
> > > > >
> > > > > Testcase: igt/gem_close
> > > > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102355
> > > > > Fixes: d1b48c1e7184 ("drm/i915: Replace execbuf vma ht with an idr")
> > > > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > > > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > > > > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > > >
> > > > <SNIP>
> > > >
> > > > > +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > > > > @@ -720,6 +720,7 @@ static int eb_lookup_vmas(struct i915_execbuffer *eb)
> > > > > goto err_obj;
> > > > > }
> > > > >
> > > > > + vma->open_count++;
> > > > > list_add(&lut->obj_link, &obj->lut_list);
> > > >
> > > > This code maybe should be in i915_gem.c as "i915_gem_object_add_lut" or
> > > > something.
> > >
> > > I disagree. It's very much tied to being an execbuf only interaction,
> > > that obj/ctx/handle.
> >
> > So how are we going to proceed here? The current proposed solution is
> > very unintuitive, one counter spread over multiple files.
>
> The table is very much for the entertainment of execbuf (and if you
> squint hard, ok not hard at all, so is the rest of GEM), if you were to
> push hard that's where I suggest to shove it.
>
> But I'm not yet seeing the issue with one side being clear where the
> user opens the vma and the other where it is closed by the user.

As long as it's in one file, all good, so execbuf is fine.

Regards, Joonas
--
Joonas Lahtinen
Open Source Technology Center
Intel Corporation