Re: [PATCH] drm/i915: Fix locking in DRRS flush/invalidate hooks

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 09 Apr 2015, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> We must acquire the mutex before we can check drrs.dp, otherwise
> someone might sneak in with a modeset, clear the pointer after we've
> checked it and then the code will Oops.
>
> This issue has been introduced in
>
> commit a93fad0f7fb8a3ff12e8814b630648f6d187954c
> Author: Vandana Kannan <vandana.kannan@intel.com>
> Date:   Sat Jan 10 02:25:59 2015 +0530
>
>     drm/i915: DRRS calls based on frontbuffer
>
> Cc: Ramalingam C <ramalingam.c@intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Vandana Kannan <vandana.kannan@intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Missed 4.0 so this is

Cc: stable@vger.kernel.org


> ---
>  drivers/gpu/drm/i915/intel_dp.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 1b87969536ff..e265a0dee479 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -5170,7 +5170,6 @@ static void intel_edp_drrs_downclock_work(struct work_struct *work)
>  			downclock_mode->vrefresh);
>  
>  unlock:
> -
>  	mutex_unlock(&dev_priv->drrs.mutex);
>  }
>  
> @@ -5192,12 +5191,14 @@ void intel_edp_drrs_invalidate(struct drm_device *dev,
>  	struct drm_crtc *crtc;
>  	enum pipe pipe;
>  
> -	if (!dev_priv->drrs.dp)
> -		return;
> -
>  	cancel_delayed_work_sync(&dev_priv->drrs.work);
>  
>  	mutex_lock(&dev_priv->drrs.mutex);
> +	if (!dev_priv->drrs.dp) {
> +		mutex_unlock(&dev_priv->drrs.mutex);
> +		return;
> +	}
> +
>  	crtc = dp_to_dig_port(dev_priv->drrs.dp)->base.base.crtc;
>  	pipe = to_intel_crtc(crtc)->pipe;
>  
> @@ -5231,12 +5232,14 @@ void intel_edp_drrs_flush(struct drm_device *dev,
>  	struct drm_crtc *crtc;
>  	enum pipe pipe;
>  
> -	if (!dev_priv->drrs.dp)
> -		return;
> -
>  	cancel_delayed_work_sync(&dev_priv->drrs.work);
>  
>  	mutex_lock(&dev_priv->drrs.mutex);
> +	if (!dev_priv->drrs.dp) {
> +		mutex_unlock(&dev_priv->drrs.mutex);
> +		return;
> +	}
> +
>  	crtc = dp_to_dig_port(dev_priv->drrs.dp)->base.base.crtc;
>  	pipe = to_intel_crtc(crtc)->pipe;
>  	dev_priv->drrs.busy_frontbuffer_bits &= ~frontbuffer_bits;
> -- 
> 2.1.4
>
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-- 
Jani Nikula, Intel Open Source Technology Center
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