[Intel-gfx] [RFC 1/8] drm/i915: Add a new PMU for handling non-OA counter data profiling requests

[Chris Wilson]

On Wed, Aug 05, 2015 at 11:25:37AM +0530, sourab.gupta at intel.com wrote:
> +static void gen_buffer_destroy(struct drm_i915_private *i915)
> +{
> +	mutex_lock(&i915->dev->struct_mutex);
> +	vunmap(i915->gen_pmu.buffer.addr);
> +	i915_gem_object_ggtt_unpin(i915->gen_pmu.buffer.obj);
> +	drm_gem_object_unreference(&i915->gen_pmu.buffer.obj->base);
> +	mutex_unlock(&i915->dev->struct_mutex);
> +
> +	spin_lock(&i915->gen_pmu.lock);
> +	i915->gen_pmu.buffer.obj = NULL;
> +	i915->gen_pmu.buffer.gtt_offset = 0;
> +	i915->gen_pmu.buffer.addr = NULL;
> +	spin_unlock(&i915->gen_pmu.lock);

This ordering looks scary. At the very least it deserves a comment to
explain why it is safe.

So what stops a second event being created while the first is being
destroyed? I presume the perf events are exclusive? Or a refcounted
singleton?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre