Re: [PATCH 1/3] drm/i915: Repeat flush of idle work during suspend

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On to, 2016-12-22 at 12:00 +0000, Chris Wilson wrote:
> The idle work handler is self-arming - if it detects that it needs to
> run again it will queue itself from its work handler. Take greater care
> when trying to drain the idle work, and double check that it is flushed.
> 
> The free worker has a similar issue where it is armed by an RCU task
> which may be running concurrently with us.
> 
> This should hopefully help with the sporadic WARN_ON(dev_priv->gt.awake)
> from i915_gem_suspend.
> 
> v2: Reuse drain_freed_objects.
> v3: Don't try to flush the freed objects from the shrinker, as it may be
> underneath the struct_mutex already.

<SNIP>

> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -3207,6 +3207,13 @@ i915_gem_object_create_from_data(struct drm_i915_private *dev_priv,
>  void i915_gem_close_object(struct drm_gem_object *gem, struct drm_file *file);
>  void i915_gem_free_object(struct drm_gem_object *obj);
>  
> +static inline void i915_gem_drain_freed_objects(struct drm_i915_private *i915)
> +{
> +	rcu_barrier();
> +	while (flush_work(&i915->mm.free_work))
> +		rcu_barrier();

Looks much like do { } while();

Also make a comment that we loop just for paranoia.

> @@ -4262,8 +4262,10 @@ int i915_gem_suspend(struct drm_i915_private *dev_priv)
>  
>  	cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work);
>  	cancel_delayed_work_sync(&dev_priv->gt.retire_work);
> -	flush_delayed_work(&dev_priv->gt.idle_work);
> -	flush_work(&dev_priv->mm.free_work);

Put a comment here that idle_work is re-arming.

> +	while (flush_delayed_work(&dev_priv->gt.idle_work))
> +		;
> +
> +	i915_gem_drain_freed_objects(dev_priv);
>  
>  	/* Assert that we sucessfully flushed all the work and
>  	 * reset the GPU back to its idle, low power state.

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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