PM / Domains: Queue up power off work only if it is not pending

In theory it is possible that pm_genpd_poweroff() for two different
subdomains of the same parent domain will attempt to queue up the
execution of pm_genpd_poweroff() for the parent twice in a row.  This
would lead to unpleasant consequences, so prevent it from happening
by checking if genpd->power_off_work is pending before attempting to
queue it up.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

drivers/base/power/domain.c

@@ -212,6 +212,19 @@ static bool genpd_abort_poweroff(struct generic_pm_domain *genpd)
 	return genpd->status == GPD_STATE_ACTIVE || genpd->resume_count > 0;
 }
 
+/**
+ * genpd_queue_power_off_work - Queue up the execution of pm_genpd_poweroff().
+ * @genpd: PM domait to power off.
+ *
+ * Queue up the execution of pm_genpd_poweroff() unless it's already been done
+ * before.
+ */
+static void genpd_queue_power_off_work(struct generic_pm_domain *genpd)
+{
+	if (!work_pending(&genpd->power_off_work))
+		queue_work(pm_wq, &genpd->power_off_work);
+}
+
 /**
  * pm_genpd_poweroff - Remove power from a given PM domain.
  * @genpd: PM domain to power down.
@@ -304,7 +317,7 @@ static int pm_genpd_poweroff(struct generic_pm_domain *genpd)
 	if (parent) {
 		genpd_sd_counter_dec(parent);
 		if (parent->sd_count == 0)
-			queue_work(pm_wq, &parent->power_off_work);
+			genpd_queue_power_off_work(parent);
 
 		genpd_release_lock(parent);
 	}