Re: [Intel-gfx] [PATCH 2/3] drm/i915/gem: Move context decoupling from postclose to preclose

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Tang, CQ (2020-07-23 18:44:08)
> 
> 
> > -----Original Message-----
> > From: Chris Wilson <chris@chris-wilson.co.uk>
> > Sent: Thursday, July 23, 2020 10:21 AM
> > To: intel-gfx@lists.freedesktop.org
> > Cc: dri-devel@lists.freedesktop.org; Chris Wilson <chris@chris-wilson.co.uk>;
> > Tang, CQ <cq.tang@intel.com>; Vetter, Daniel <daniel.vetter@intel.com>;
> > stable@vger.kernel.org
> > Subject: [PATCH 2/3] drm/i915/gem: Move context decoupling from
> > postclose to preclose
> > 
> > Since the GEM contexts refer to other GEM state, we need to nerf those
> > pointers before that state is freed during drm_gem_release(). We need to
> > move i915_gem_context_close() from the postclose callback to the preclose.
> > 
> > In particular, debugfs likes to peek into the GEM contexts, and from there
> > peek at the drm core objects. If the context is closed during the peeking, we
> > may attempt to dereference a stale core object.
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: CQ Tang <cq.tang@intel.com>
> > Cc: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: stable@vger.kernel.org
> > ---
> >  drivers/gpu/drm/i915/i915_drv.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c
> > b/drivers/gpu/drm/i915/i915_drv.c index 5fd5af4bc855..15242a8c70f7 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -1114,11 +1114,15 @@ static void i915_driver_lastclose(struct
> > drm_device *dev)
> >       vga_switcheroo_process_delayed_switch();
> >  }
> > 
> > +static void i915_driver_preclose(struct drm_device *dev, struct
> > +drm_file *file) {
> > +     i915_gem_context_close(file);
> > +}
> > +
> >  static void i915_driver_postclose(struct drm_device *dev, struct drm_file
> > *file)  {
> >       struct drm_i915_file_private *file_priv = file->driver_priv;
> > 
> > -     i915_gem_context_close(file);
> >       i915_gem_release(dev, file);
> 
> Now we separate i915_gem_context_close() from i915_gem_release() and other freeing code in postclose(), is there any side effect to allow code to run in between?
> Can we move all postclose() code into preclose()?

i915_gem_release() is scheduled for deletion, so I didn't care. What
remains in postclose are the kfree + tidyup, which seem like a good idea
to keep last.
-Chris
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