Input: serio - convert to common workqueue instead of a thread

Instead of creating an exclusive thread to handle serio events (which
happen rarely), let's switch to using common workqueue. With the arrival
of concurrency-managed workqueue infrastructure we are not concerned
that our callers or callees also using workqueue (no deadlocks anymore)
and it should reduce total number of threads in the system.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

diff --git a/drivers/input/serio/serio.c b/drivers/input/serio/serio.c
index 405bf21..db5b0bc 100644 (file)
--- a/drivers/input/serio/serio.c
+++ b/drivers/input/serio/serio.c
@@ -32,10 +32,9 @@
 #include <linux/module.h>
 #include <linux/serio.h>
 #include <linux/errno.h>
-#include <linux/wait.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
-#include <linux/kthread.h>
+#include <linux/workqueue.h>
 #include <linux/mutex.h>
 
 MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
@@ -44,7 +43,7 @@ MODULE_LICENSE("GPL");
 
 /*
  * serio_mutex protects entire serio subsystem and is taken every time
- * serio port or driver registrered or unregistered.
+ * serio port or driver registered or unregistered.
  */
 static DEFINE_MUTEX(serio_mutex);
 
@@ -165,58 +164,22 @@ struct serio_event {
 
 static DEFINE_SPINLOCK(serio_event_lock);      /* protects serio_event_list */
 static LIST_HEAD(serio_event_list);
-static DECLARE_WAIT_QUEUE_HEAD(serio_wait);
-static struct task_struct *serio_task;
 
-static int serio_queue_event(void *object, struct module *owner,
-                            enum serio_event_type event_type)
+static struct serio_event *serio_get_event(void)
 {
+       struct serio_event *event = NULL;
        unsigned long flags;
-       struct serio_event *event;
-       int retval = 0;
 
        spin_lock_irqsave(&serio_event_lock, flags);
 
-       /*
-        * Scan event list for the other events for the same serio port,
-        * starting with the most recent one. If event is the same we
-        * do not need add new one. If event is of different type we
-        * need to add this event and should not look further because
-        * we need to preseve sequence of distinct events.
-        */
-       list_for_each_entry_reverse(event, &serio_event_list, node) {
-               if (event->object == object) {
-                       if (event->type == event_type)
-                               goto out;
-                       break;
-               }
-       }
-
-       event = kmalloc(sizeof(struct serio_event), GFP_ATOMIC);
-       if (!event) {
-               pr_err("Not enough memory to queue event %d\n", event_type);
-               retval = -ENOMEM;
-               goto out;
-       }
-
-       if (!try_module_get(owner)) {
-               pr_warning("Can't get module reference, dropping event %d\n",
-                          event_type);
-               kfree(event);
-               retval = -EINVAL;
-               goto out;
+       if (!list_empty(&serio_event_list)) {
+               event = list_first_entry(&serio_event_list,
+                                        struct serio_event, node);
+               list_del_init(&event->node);
        }
 
-       event->type = event_type;
-       event->object = object;
-       event->owner = owner;
-
-       list_add_tail(&event->node, &serio_event_list);
-       wake_up(&serio_wait);
-
-out:
        spin_unlock_irqrestore(&serio_event_lock, flags);
-       return retval;
+       return event;
 }
 
 static void serio_free_event(struct serio_event *event)
@@ -250,25 +213,7 @@ static void serio_remove_duplicate_events(struct serio_event *event)
        spin_unlock_irqrestore(&serio_event_lock, flags);
 }
 
-
-static struct serio_event *serio_get_event(void)
-{
-       struct serio_event *event = NULL;
-       unsigned long flags;
-
-       spin_lock_irqsave(&serio_event_lock, flags);
-
-       if (!list_empty(&serio_event_list)) {
-               event = list_first_entry(&serio_event_list,
-                                        struct serio_event, node);
-               list_del_init(&event->node);
-       }
-
-       spin_unlock_irqrestore(&serio_event_lock, flags);
-       return event;
-}
-
-static void serio_handle_event(void)
+static void serio_handle_event(struct work_struct *work)
 {
        struct serio_event *event;
 
@@ -307,6 +252,59 @@ static void serio_handle_event(void)
        mutex_unlock(&serio_mutex);
 }
 
+static DECLARE_WORK(serio_event_work, serio_handle_event);
+
+static int serio_queue_event(void *object, struct module *owner,
+                            enum serio_event_type event_type)
+{
+       unsigned long flags;
+       struct serio_event *event;
+       int retval = 0;
+
+       spin_lock_irqsave(&serio_event_lock, flags);
+
+       /*
+        * Scan event list for the other events for the same serio port,
+        * starting with the most recent one. If event is the same we
+        * do not need add new one. If event is of different type we
+        * need to add this event and should not look further because
+        * we need to preseve sequence of distinct events.
+        */
+       list_for_each_entry_reverse(event, &serio_event_list, node) {
+               if (event->object == object) {
+                       if (event->type == event_type)
+                               goto out;
+                       break;
+               }
+       }
+
+       event = kmalloc(sizeof(struct serio_event), GFP_ATOMIC);
+       if (!event) {
+               pr_err("Not enough memory to queue event %d\n", event_type);
+               retval = -ENOMEM;
+               goto out;
+       }
+
+       if (!try_module_get(owner)) {
+               pr_warning("Can't get module reference, dropping event %d\n",
+                          event_type);
+               kfree(event);
+               retval = -EINVAL;
+               goto out;
+       }
+
+       event->type = event_type;
+       event->object = object;
+       event->owner = owner;
+
+       list_add_tail(&event->node, &serio_event_list);
+       schedule_work(&serio_event_work);
+
+out:
+       spin_unlock_irqrestore(&serio_event_lock, flags);
+       return retval;
+}
+
 /*
  * Remove all events that have been submitted for a given
  * object, be it serio port or driver.
@@ -356,18 +354,6 @@ static struct serio *serio_get_pending_child(struct serio *parent)
        return child;
 }
 
-static int serio_thread(void *nothing)
-{
-       do {
-               serio_handle_event();
-               wait_event_interruptible(serio_wait,
-                       kthread_should_stop() || !list_empty(&serio_event_list));
-       } while (!kthread_should_stop());
-
-       return 0;
-}
-
-
 /*
  * Serio port operations
  */
@@ -1040,21 +1026,18 @@ static int __init serio_init(void)
                return error;
        }
 
-       serio_task = kthread_run(serio_thread, NULL, "kseriod");
-       if (IS_ERR(serio_task)) {
-               bus_unregister(&serio_bus);
-               error = PTR_ERR(serio_task);
-               pr_err("Failed to start kseriod, error: %d\n", error);
-               return error;
-       }
-
        return 0;
 }
 
 static void __exit serio_exit(void)
 {
        bus_unregister(&serio_bus);
-       kthread_stop(serio_task);
+
+       /*
+        * There should not be any outstanding events but work may
+        * still be scheduled so simply cancel it.
+        */
+       cancel_work_sync(&serio_event_work);
 }
 
 subsys_initcall(serio_init);