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

From: Mauro Carvalho Chehab <m.chehab@samsung.com>
To: "David Härdeman" <david@hardeman.nu>
Cc: linux-media@vger.kernel.org
Subject: Re: [PATCH 40/49] rc-ir-raw: simplify locking
Date: Fri, 25 Jul 2014 20:08:52 -0300	[thread overview]
Message-ID: <20140725200852.1aa56c69.m.chehab@samsung.com> (raw)
In-Reply-To: <20140403233438.27099.1183.stgit@zeus.muc.hardeman.nu>

Em Fri, 04 Apr 2014 01:34:38 +0200
David Härdeman <david@hardeman.nu> escreveu:

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

Please rebase.

> 
> 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);
>  
> 
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