Re: [PATCH 1/2] drm/i915: fix possible RPM ref leaking during RPS disabling

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, May 12, 2014 at 06:35:04PM +0300, Imre Deak wrote:
> In
> 
> commit c6df39b5ea6342323a42edfbeeca0a28c643d7ae
> Author: Imre Deak <imre.deak@intel.com>
> Date:   Mon Apr 14 20:24:29 2014 +0300
> 
>     drm/i915: get a runtime PM ref for the deferred GT powersave enabling
> 
> I added an RPM get-ref when enabling RPS from a deferred work, but forgot
> to add the corresponding put-ref when canceling the work. This may leave
> RPM disabled.
> 
> Signed-off-by: Imre Deak <imre.deak@intel.com>

Could we intentionally hit this by e.g. racing a suspend/resume against
runtime pm? E.g.
1. disable all outputs, make sure we've entered runtime pm
2. set runtime autosuspend delay to 0
3. suspend/resume
4. autosuspend (hopefully, my understanding is a bit unclear)

->Boom

Would look nice as an igt subtest if it works ;-)
-Daniel

> ---
>  drivers/gpu/drm/i915/intel_pm.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 834c49c..9170039 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4609,7 +4609,9 @@ void intel_disable_gt_powersave(struct drm_device *dev)
>  		ironlake_disable_drps(dev);
>  		ironlake_disable_rc6(dev);
>  	} else if (IS_GEN6(dev) || IS_GEN7(dev)) {
> -		cancel_delayed_work_sync(&dev_priv->rps.delayed_resume_work);
> +		if (cancel_delayed_work_sync(&dev_priv->rps.delayed_resume_work))
> +			intel_runtime_pm_put(dev_priv);
> +
>  		cancel_work_sync(&dev_priv->rps.work);
>  		mutex_lock(&dev_priv->rps.hw_lock);
>  		if (IS_VALLEYVIEW(dev))
> -- 
> 1.8.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch