async: Introduce async_schedule_dev_nocall()

In preparation for subsequent changes, introduce a specialized variant
of async_schedule_dev() that will not invoke the argument function
synchronously when it cannot be scheduled for asynchronous execution.

The new function, async_schedule_dev_nocall(), will be used for fixing
possible deadlocks in the system-wide power management core code.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com> for the series.
Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

include/linux/async.h

@@ -90,6 +90,8 @@ async_schedule_dev(async_func_t func, struct device *dev)
 	return async_schedule_node(func, dev, dev_to_node(dev));
 }
 
+bool async_schedule_dev_nocall(async_func_t func, struct device *dev);
+
 /**
  * async_schedule_dev_domain - A device specific version of async_schedule_domain
  * @func: function to execute asynchronously

kernel/async.c

@@ -243,6 +243,35 @@ async_cookie_t async_schedule_node(async_func_t func, void *data, int node)
 }
 EXPORT_SYMBOL_GPL(async_schedule_node);
 
+/**
+ * async_schedule_dev_nocall - A simplified variant of async_schedule_dev()
+ * @func: function to execute asynchronously
+ * @dev: device argument to be passed to function
+ *
+ * @dev is used as both the argument for the function and to provide NUMA
+ * context for where to run the function.
+ *
+ * If the asynchronous execution of @func is scheduled successfully, return
+ * true. Otherwise, do nothing and return false, unlike async_schedule_dev()
+ * that will run the function synchronously then.
+ */
+bool async_schedule_dev_nocall(async_func_t func, struct device *dev)
+{
+	struct async_entry *entry;
+
+	entry = kzalloc(sizeof(struct async_entry), GFP_KERNEL);
+
+	/* Give up if there is no memory or too much work. */
+	if (!entry || atomic_read(&entry_count) > MAX_WORK) {
+		kfree(entry);
+		return false;
+	}
+
+	__async_schedule_node_domain(func, dev, dev_to_node(dev),
+				     &async_dfl_domain, entry);
+	return true;
+}
+
 /**
  * async_synchronize_full - synchronize all asynchronous function calls
  *