[PATCH 1/2] drm/i915/pmu: Handle PCI unbind

[Chris Wilson]

Quoting Tvrtko Ursulin (2020-10-16 10:30:50)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Mark the device as closed and keep references to driver data alive to
> allow for safe driver unbind with active PMU clients. Perf core does not
> otherwise handle this case so we have to do it manually like this.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
> @@ -1167,7 +1196,13 @@ void i915_pmu_unregister(struct drm_i915_private *i915)
>         if (!pmu->base.event_init)
>                 return;
>  
> -       drm_WARN_ON(&i915->drm, pmu->enable);
> +       /*
> +        * "Disconnect" the PMU callbacks - since all are atomic synchronize_rcu
> +        * ensures all currently executing ones will have exited before we
> +        * proceed with unregistration.
> +        */
> +       pmu->closed = true;
> +       synchronize_rcu();

This reminds me of drm_dev_unplug. I think the argument that this
interoperates with the perf API using RCU (rather than SRCU) justifies
the distinction.

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris