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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Greg KH <gregkh@linuxfoundation.org>, linux-pm@vger.kernel.org
Cc: Youngmin Nam <youngmin.nam@samsung.com>, rafael@kernel.org, linux-kernel@vger.kernel.org, d7271.choe@samsung.com, janghyuck.kim@samsung.com, hyesoo.yu@samsung.com, Alan Stern <stern@rowland.harvard.edu>, Ulf Hansson <ulf.hansson@linaro.org>
Subject: [PATCH v1 2/3] async: Introduce async_schedule_dev_nocall()
Date: Wed, 27 Dec 2023 21:38:23 +0100
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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>
---
 drivers/base/power/main.c |   12 ++++++++----
 include/linux/async.h     |    2 ++
 kernel/async.c            |   29 +++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+), 4 deletions(-)

Index: linux-pm/kernel/async.c
===================================================================
--- linux-pm.orig/kernel/async.c
+++ linux-pm/kernel/async.c
@@ -244,6 +244,35 @@ async_cookie_t async_schedule_node(async
 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
  *
  * This function waits until all asynchronous function calls have been done.
Index: linux-pm/include/linux/async.h
===================================================================
--- linux-pm.orig/include/linux/async.h
+++ linux-pm/include/linux/async.h
@@ -90,6 +90,8 @@ async_schedule_dev(async_func_t func, st
 	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