ALSA: hda: Fix racy display power access

snd_hdac_display_power() doesn't handle the concurrent calls carefully
enough, and it may lead to the doubly get_power or put_power calls,
when a runtime PM and an async work get called in racy way.

This patch addresses it by reusing the bus->lock mutex that has been
used for protecting the link state change in ext bus code, so that it
can protect against racy display state changes.  The initialization of
bus->lock was moved from snd_hdac_ext_bus_init() to
snd_hdac_bus_init() as well accordingly.

Testcase: igt/i915_pm_rpm/module-reload #glk-dsi
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/s5h8swiunph.wl-tiwai@suse.de

sound/hda/ext/hdac_ext_bus.c

@@ -107,7 +107,6 @@ int snd_hdac_ext_bus_init(struct hdac_bus *bus, struct device *dev,
 	INIT_LIST_HEAD(&bus->hlink_list);
 	bus->idx = idx++;
 
-	mutex_init(&bus->lock);
 	bus->cmd_dma_state = true;
 
 	return 0;

sound/hda/hdac_bus.c

@@ -38,6 +38,7 @@ int snd_hdac_bus_init(struct hdac_bus *bus, struct device *dev,
 	INIT_WORK(&bus->unsol_work, snd_hdac_bus_process_unsol_events);
 	spin_lock_init(&bus->reg_lock);
 	mutex_init(&bus->cmd_mutex);
+	mutex_init(&bus->lock);
 	bus->irq = -1;
 	return 0;
 }

sound/hda/hdac_component.c

@@ -69,13 +69,15 @@ void snd_hdac_display_power(struct hdac_bus *bus, unsigned int idx, bool enable)
 
 	dev_dbg(bus->dev, "display power %s\n",
 		enable ? "enable" : "disable");
+
+	mutex_lock(&bus->lock);
 	if (enable)
 		set_bit(idx, &bus->display_power_status);
 	else
 		clear_bit(idx, &bus->display_power_status);
 
 	if (!acomp || !acomp->ops)
-		return;
+		goto unlock;
 
 	if (bus->display_power_status) {
 		if (!bus->display_power_active) {
@@ -98,6 +100,8 @@ void snd_hdac_display_power(struct hdac_bus *bus, unsigned int idx, bool enable)
 			bus->display_power_active = 0;
 		}
 	}
+ unlock:
+	mutex_unlock(&bus->lock);
 }
 EXPORT_SYMBOL_GPL(snd_hdac_display_power);