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

[Tang, CQ]

> -----Original Message-----
> From: Chris Wilson <chris at chris-wilson.co.uk>
> Sent: Thursday, July 23, 2020 10:21 AM
> To: intel-gfx at lists.freedesktop.org
> Cc: dri-devel at lists.freedesktop.org; Chris Wilson <chris at chris-wilson.co.uk>;
> Tang, CQ <cq.tang at intel.com>; Vetter, Daniel <daniel.vetter at intel.com>;
> stable at 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 at chris-wilson.co.uk>
> Cc: CQ Tang <cq.tang at intel.com>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: stable at 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()?

--CQ

> 
>  	kfree_rcu(file_priv, rcu);
> @@ -1850,6 +1854,7 @@ static struct drm_driver driver = {
>  	.release = i915_driver_release,
>  	.open = i915_driver_open,
>  	.lastclose = i915_driver_lastclose,
> +	.preclose  = i915_driver_preclose,
>  	.postclose = i915_driver_postclose,
> 
>  	.gem_close_object = i915_gem_close_object,
> --
> 2.20.1