[Intel-gfx] [PATCH] drm/i915: Fixing mutex deadlock window at eDP DRRS

[Rodrigo Vivi]

Looks enough for me...

Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>

On Mon, Mar 2, 2015 at 10:41 PM, Ramalingam C <ramalingam.c at intel.com> wrote:
> In invalidate and flush functions of eDP DRRS, if deferred downclock
> work starts execution at a time window between acquiring the drrs
> mutex and cancellation of the deferred work
> (intel_edp_drrs_downclock_work), then deferred work will find
> drrs mutex locked and wait for the same.
>
> Meanwhile the function that acquired mutex drrs invalidate/flush will
> wait for the completion of the deferred work before releasing the mutex.
> Thats a deadlock.
>
> To avoid such deadlock scenario, this change cancels the deferred work
> before acquiring the mutex at invalidate and flush functions.
>
> Signed-off-by: Ramalingam C <ramalingam.c at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index d1141d3..0a57763 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -4966,12 +4966,13 @@ void intel_edp_drrs_invalidate(struct drm_device *dev,
>         if (!dev_priv->drrs.dp)
>                 return;
>
> +       cancel_delayed_work_sync(&dev_priv->drrs.work);
> +
>         mutex_lock(&dev_priv->drrs.mutex);
>         crtc = dp_to_dig_port(dev_priv->drrs.dp)->base.base.crtc;
>         pipe = to_intel_crtc(crtc)->pipe;
>
>         if (dev_priv->drrs.refresh_rate_type == DRRS_LOW_RR) {
> -               cancel_delayed_work_sync(&dev_priv->drrs.work);
>                 intel_dp_set_drrs_state(dev_priv->dev,
>                                 dev_priv->drrs.dp->attached_connector->panel.
>                                 fixed_mode->vrefresh);
> @@ -5004,13 +5005,13 @@ void intel_edp_drrs_flush(struct drm_device *dev,
>         if (!dev_priv->drrs.dp)
>                 return;
>
> +       cancel_delayed_work_sync(&dev_priv->drrs.work);
> +
>         mutex_lock(&dev_priv->drrs.mutex);
>         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;
>
> -       cancel_delayed_work_sync(&dev_priv->drrs.work);
> -
>         if (dev_priv->drrs.refresh_rate_type != DRRS_LOW_RR &&
>                         !dev_priv->drrs.busy_frontbuffer_bits)
>                 schedule_delayed_work(&dev_priv->drrs.work,
> --
> 1.7.9.5
>
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-- 
Rodrigo Vivi
Blog: http://blog.vivi.eng.br