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Date:   Mon, 15 Apr 2019 11:32:25 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Janusz Krzysztofik <janusz.krzysztofik@...ux.intel.com>
Cc:     Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        michal.wajdeczko@...el.com, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Janusz Krzysztofik <janusz.krzysztofik@...el.com>
Subject: Re: [PATCH 1/2] drm/i915: Use drm_dev_unplug()

On Fri, Apr 05, 2019 at 03:02:34PM +0200, Janusz Krzysztofik wrote:
> From: Janusz Krzysztofik <janusz.krzysztofik@...el.com>
> 
> 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.  Once done, also cancel inflight operations immediately by
> calling i915_gem_set_wedged().
> 
> Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@...el.com>
> Reviewed-by: Chris Wilson <chris@...is-wilson.co.uk>

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>

> ---
>  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);
>  
>  	i915_gem_shrinker_unregister(dev_priv);
>  }
> -- 
> 2.20.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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