[PATCH 40/49] rc-ir-raw: simplify locking

["David Härdeman" <david@hardeman.nu>]

Simplify and improve the locking in rc-ir-raw by making better use of
the existing kfifo functionality and by using RCU where possible.

Signed-off-by: David Härdeman <david@hardeman.nu>
---
 drivers/media/rc/rc-core-priv.h |    6 +-
 drivers/media/rc/rc-ir-raw.c    |  124 ++++++++++++++++-----------------------
 2 files changed, 55 insertions(+), 75 deletions(-)

diff --git a/drivers/media/rc/rc-core-priv.h b/drivers/media/rc/rc-core-priv.h
index 0b32ef8..c3de26b 100644
--- a/drivers/media/rc/rc-core-priv.h
+++ b/drivers/media/rc/rc-core-priv.h
@@ -37,11 +37,13 @@ struct ir_raw_handler {
 	int (*raw_unregister)(struct rc_dev *dev);
 };
 
+/* max number of pulse/space transitions to buffer */
+#define RC_MAX_IR_EVENTS	512
+
 struct ir_raw_event_ctrl {
 	struct list_head		list;		/* to keep track of raw clients */
 	struct task_struct		*thread;
-	spinlock_t			lock;
-	struct kfifo_rec_ptr_1		kfifo;		/* fifo for the pulse/space durations */
+	DECLARE_KFIFO(kfifo, struct ir_raw_event, RC_MAX_IR_EVENTS); /* for pulse/space durations */
 	ktime_t				last_event;	/* when last event occurred */
 	enum raw_event_type		last_type;	/* last event type */
 	struct rc_dev			*dev;		/* pointer to the parent rc_dev */
diff --git a/drivers/media/rc/rc-ir-raw.c b/drivers/media/rc/rc-ir-raw.c
index 86f5aa7..9631825 100644
--- a/drivers/media/rc/rc-ir-raw.c
+++ b/drivers/media/rc/rc-ir-raw.c
@@ -21,15 +21,12 @@
 #include <linux/freezer.h>
 #include "rc-core-priv.h"
 
-/* Define the max number of pulse/space transitions to buffer */
-#define MAX_IR_EVENT_SIZE      512
-
-/* Used to keep track of IR raw clients, protected by ir_raw_handler_lock */
+/* IR raw clients/handlers, writers synchronize with ir_raw_mutex */
+static DEFINE_MUTEX(ir_raw_mutex);
 static LIST_HEAD(ir_raw_client_list);
-
-/* Used to handle IR raw handler extensions */
-static DEFINE_MUTEX(ir_raw_handler_lock);
 static LIST_HEAD(ir_raw_handler_list);
+
+/* protocols supported by the currently loaded decoders */
 static u64 available_protocols;
 
 static int ir_raw_event_thread(void *data)
@@ -37,32 +34,19 @@ static int ir_raw_event_thread(void *data)
 	struct ir_raw_event ev;
 	struct ir_raw_handler *handler;
 	struct ir_raw_event_ctrl *raw = (struct ir_raw_event_ctrl *)data;
-	int retval;
 
 	while (!kthread_should_stop()) {
-
-		spin_lock_irq(&raw->lock);
-		retval = kfifo_len(&raw->kfifo);
-
-		if (retval < sizeof(ev)) {
+		if (kfifo_out(&raw->kfifo, &ev, 1) == 0) {
 			set_current_state(TASK_INTERRUPTIBLE);
-
-			if (kthread_should_stop())
-				set_current_state(TASK_RUNNING);
-
-			spin_unlock_irq(&raw->lock);
 			schedule();
 			continue;
 		}
 
-		retval = kfifo_out(&raw->kfifo, &ev, sizeof(ev));
-		spin_unlock_irq(&raw->lock);
-
-		mutex_lock(&ir_raw_handler_lock);
-		list_for_each_entry(handler, &ir_raw_handler_list, list)
+		rcu_read_lock();
+		list_for_each_entry_rcu(handler, &ir_raw_handler_list, list)
 			handler->decode(raw->dev, ev);
+		rcu_read_unlock();
 		raw->prev_ev = ev;
-		mutex_unlock(&ir_raw_handler_lock);
 	}
 
 	return 0;
@@ -76,7 +60,8 @@ static int ir_raw_event_thread(void *data)
  * This routine (which may be called from an interrupt context) stores a
  * pulse/space duration for the raw ir decoding state machines. Pulses are
  * signalled as positive values and spaces as negative values. A zero value
- * will reset the decoding state machines.
+ * will reset the decoding state machines. Drivers are responsible for
+ * synchronizing calls to this function.
  */
 int ir_raw_event_store(struct rc_dev *dev, struct ir_raw_event *ev)
 {
@@ -86,7 +71,7 @@ int ir_raw_event_store(struct rc_dev *dev, struct ir_raw_event *ev)
 	IR_dprintk(2, "sample: (%05dus %s)\n",
 		   TO_US(ev->duration), TO_STR(ev->pulse));
 
-	if (kfifo_in(&dev->raw->kfifo, ev, sizeof(*ev)) != sizeof(*ev))
+	if (kfifo_in(&dev->raw->kfifo, ev, 1) != 1)
 		return -ENOMEM;
 
 	return 0;
@@ -258,14 +243,8 @@ EXPORT_SYMBOL_GPL(ir_raw_get_tx_event);
  */
 void ir_raw_event_handle(struct rc_dev *dev)
 {
-	unsigned long flags;
-
-	if (!dev->raw)
-		return;
-
-	spin_lock_irqsave(&dev->raw->lock, flags);
-	wake_up_process(dev->raw->thread);
-	spin_unlock_irqrestore(&dev->raw->lock, flags);
+	if (dev->raw)
+		wake_up_process(dev->raw->thread);
 }
 EXPORT_SYMBOL_GPL(ir_raw_event_handle);
 
@@ -273,9 +252,9 @@ EXPORT_SYMBOL_GPL(ir_raw_event_handle);
 static u64 ir_raw_get_allowed_protocols(struct rc_dev *dev)
 {
 	u64 protocols;
-	mutex_lock(&ir_raw_handler_lock);
+	mutex_lock(&ir_raw_mutex);
 	protocols = available_protocols;
-	mutex_unlock(&ir_raw_handler_lock);
+	mutex_unlock(&ir_raw_mutex);
 	return protocols;
 }
 
@@ -290,52 +269,49 @@ static int change_protocol(struct rc_dev *dev, u64 *rc_type) {
 int rc_register_ir_raw_device(struct rc_dev *dev)
 {
 	int rc;
+	struct ir_raw_event_ctrl *raw;
 	struct ir_raw_handler *handler;
 
 	if (!dev)
 		return -EINVAL;
 
-	dev->raw = kzalloc(sizeof(*dev->raw), GFP_KERNEL);
-	if (!dev->raw)
+	raw = kzalloc(sizeof(*raw), GFP_KERNEL);
+	if (!raw)
 		return -ENOMEM;
 
-	dev->raw->dev = dev;
-	dev->enabled_protocols = ~0;
-	dev->get_protocols = ir_raw_get_allowed_protocols;
-	dev->driver_type = RC_DRIVER_IR_RAW;
-	dev->change_protocol = change_protocol;
-	spin_lock_init(&dev->raw->lock);
-	rc = kfifo_alloc(&dev->raw->kfifo,
-			 sizeof(struct ir_raw_event) * MAX_IR_EVENT_SIZE,
-			 GFP_KERNEL);
-	if (rc < 0)
-		goto out;
-
-	dev->raw->thread = kthread_run(ir_raw_event_thread, dev->raw,
-				       dev_name(&dev->dev));
+	raw->dev = dev;
+	INIT_KFIFO(raw->kfifo);
+	raw->thread = kthread_run(ir_raw_event_thread, dev->raw,
+				  dev_name(&dev->dev));
 
-	if (IS_ERR(dev->raw->thread)) {
-		rc = PTR_ERR(dev->raw->thread);
+	if (IS_ERR(raw->thread)) {
+		rc = PTR_ERR(raw->thread);
 		goto out;
 	}
 
+	dev->raw = raw;
+	dev->enabled_protocols = ~0;
+	dev->get_protocols = ir_raw_get_allowed_protocols;
+	dev->driver_type = RC_DRIVER_IR_RAW;
+	dev->change_protocol = change_protocol;
 	rc = rc_register_device(dev);
 	if (rc < 0)
 		goto out_thread;
 
-	mutex_lock(&ir_raw_handler_lock);
-	list_add_tail(&dev->raw->list, &ir_raw_client_list);
-	list_for_each_entry(handler, &ir_raw_handler_list, list)
+	mutex_lock(&ir_raw_mutex);
+	list_add_tail_rcu(&dev->raw->list, &ir_raw_client_list);
+	list_for_each_entry_rcu(handler, &ir_raw_handler_list, list)
 		if (handler->raw_register)
 			handler->raw_register(dev);
-	mutex_unlock(&ir_raw_handler_lock);
+	mutex_unlock(&ir_raw_mutex);
+	synchronize_rcu();
 
 	return 0;
 
 out_thread:
-	kthread_stop(dev->raw->thread);
+	kthread_stop(raw->thread);
 out:
-	kfree(dev->raw);
+	kfree(raw);
 	dev->raw = NULL;
 	return rc;
 }
@@ -350,14 +326,14 @@ void rc_unregister_ir_raw_device(struct rc_dev *dev)
 
 	kthread_stop(dev->raw->thread);
 
-	mutex_lock(&ir_raw_handler_lock);
-	list_del(&dev->raw->list);
-	list_for_each_entry(handler, &ir_raw_handler_list, list)
+	mutex_lock(&ir_raw_mutex);
+	list_del_rcu(&dev->raw->list);
+	list_for_each_entry_rcu(handler, &ir_raw_handler_list, list)
 		if (handler->raw_unregister)
 			handler->raw_unregister(dev);
-	mutex_unlock(&ir_raw_handler_lock);
+	mutex_unlock(&ir_raw_mutex);
+	synchronize_rcu();
 
-	kfifo_free(&dev->raw->kfifo);
 	kfree(dev->raw);
 	dev->raw = NULL;
 	rc_unregister_device(dev);
@@ -372,13 +348,14 @@ int ir_raw_handler_register(struct ir_raw_handler *ir_raw_handler)
 {
 	struct ir_raw_event_ctrl *raw;
 
-	mutex_lock(&ir_raw_handler_lock);
-	list_add_tail(&ir_raw_handler->list, &ir_raw_handler_list);
+	mutex_lock(&ir_raw_mutex);
+	list_add_tail_rcu(&ir_raw_handler->list, &ir_raw_handler_list);
 	if (ir_raw_handler->raw_register)
-		list_for_each_entry(raw, &ir_raw_client_list, list)
+		list_for_each_entry_rcu(raw, &ir_raw_client_list, list)
 			ir_raw_handler->raw_register(raw->dev);
 	available_protocols |= ir_raw_handler->protocols;
-	mutex_unlock(&ir_raw_handler_lock);
+	mutex_unlock(&ir_raw_mutex);
+	synchronize_rcu();
 
 	return 0;
 }
@@ -388,13 +365,14 @@ void ir_raw_handler_unregister(struct ir_raw_handler *ir_raw_handler)
 {
 	struct ir_raw_event_ctrl *raw;
 
-	mutex_lock(&ir_raw_handler_lock);
-	list_del(&ir_raw_handler->list);
+	mutex_lock(&ir_raw_mutex);
+	list_del_rcu(&ir_raw_handler->list);
 	if (ir_raw_handler->raw_unregister)
-		list_for_each_entry(raw, &ir_raw_client_list, list)
+		list_for_each_entry_rcu(raw, &ir_raw_client_list, list)
 			ir_raw_handler->raw_unregister(raw->dev);
 	available_protocols &= ~ir_raw_handler->protocols;
-	mutex_unlock(&ir_raw_handler_lock);
+	mutex_unlock(&ir_raw_mutex);
+	synchronize_rcu();
 }
 EXPORT_SYMBOL(ir_raw_handler_unregister);