Re: [PATCH] drm/i915: Use drm_dev_unplug()

[Janusz Krzysztofik]

On Fri, 2019-04-05 at 08:41 +0100, Chris Wilson wrote:
> Quoting Janusz Krzysztofik (2019-04-05 08:26:57)
> > From: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxx>
> > 
> > The driver does not currently support unbinding from a device which
> > is
> > in use.  Since open file descriptors may still be pointing into
> > kernel
> > memory where the device structures used to be, entirely correct
> > kernel
> > panics protect the driver from being unbound as we should not be
> > unbinding it before those dangling pointers have been made safe.
> > 
> > According to the documentation found inside
> > drivers/gpu/drm/drm_drv.c,
> > drm_dev_unplug() should be used instead of drm_dev_unregister() in
> > order to make a device inaccessible to users as soon as it is
> > unpluged.
> > Follow that advice to make those possibly dangling pointers safe,
> > protected by DRM layer from a user who is otherwise left pointing
> > into
> > possibly reused kernel memory after the driver has been unbound
> > from
> > the device.
> > 
> > Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxx>
> > ---
> >  drivers/gpu/drm/i915/i915_drv.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c
> > b/drivers/gpu/drm/i915/i915_drv.c
> > index 9df65d386d11..66163378c481 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -1596,7 +1596,7 @@ static void i915_driver_unregister(struct
> > drm_i915_private *dev_priv)
> >         i915_pmu_unregister(dev_priv);
> >  
> >         i915_teardown_sysfs(dev_priv);
> > -       drm_dev_unregister(&dev_priv->drm);
> > +       drm_dev_unplug(&dev_priv->drm);
> 
> I think we may have our onion inverted here. We want to stop the
> users
> as the first step, then start removing the entries. (That will also
> nicely invert the order from register, which is what we typically
> expect).
> 
> After calling i915_driver_unregister(); call i915_gem_set_wedged() to
> immediately (give or take external fences) cancel inflight
> operations.

OK, thanks.  Do you prefer them squashed or as serparate patches?

Thanks,
Janusz

> -Chris
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