Re: [PATCH] ipmi: use rcu lock for using command receivers

["Paul E. McKenney" <paulmck@us.ibm.com>]

On Fri, Oct 28, 2005 at 08:19:44AM -0500, Corey Minyard wrote:
> I finally got some time to think this through and test it.
> This patch is in addition to the ipmi-use-refcount-in-message-handler
> patch.
> Thanks again, Paul, for seeing this.
> 
> Use rcu_read_lock for the cmd_rcvrs list, since that was what
> what intended, anyway.  This means that all the users of the
> cmd_rcvrs_lock are tasks, so the irq disables are no longer
> required for that lock and it can become a semaphore.

Looks good from an RCU viewpoint!  I presume that find_cmd_rcvr()
still includes an rcu_dereference().

						Thanx, Paul

Acked-by: <paulmck@us.ibm.com>

> Signed-off-by: Corey Minyard <minyard@acm.org>
> 
> Index: linux-2.6.14-rc4/drivers/char/ipmi/ipmi_msghandler.c
> ===================================================================
> --- linux-2.6.14-rc4.orig/drivers/char/ipmi/ipmi_msghandler.c
> +++ linux-2.6.14-rc4/drivers/char/ipmi/ipmi_msghandler.c
> @@ -209,7 +209,7 @@ struct ipmi_smi
>  
>  	/* The list of command receivers that are registered for commands
>  	   on this interface. */
> -	spinlock_t       cmd_rcvrs_lock;
> +	struct semaphore cmd_rcvrs_lock;
>  	struct list_head cmd_rcvrs;
>  
>  	/* Events that were queues because no one was there to receive
> @@ -345,7 +345,6 @@ static void clean_up_interface_data(ipmi
>  {
>  	int              i;
>  	struct cmd_rcvr  *rcvr, *rcvr2;
> -	unsigned long    flags;
>  	struct list_head list;
>  
>  	free_recv_msg_list(&intf->waiting_msgs);
> @@ -353,10 +352,10 @@ static void clean_up_interface_data(ipmi
>  
>  	/* Wholesale remove all the entries from the list in the
>  	 * interface and wait for RCU to know that none are in use. */
> -	spin_lock_irqsave(&intf->cmd_rcvrs_lock, flags);
> +	down(&intf->cmd_rcvrs_lock);
>  	list_add_rcu(&list, &intf->cmd_rcvrs);
>  	list_del_rcu(&intf->cmd_rcvrs);
> -	spin_unlock_irqrestore(&intf->cmd_rcvrs_lock, flags);
> +	up(&intf->cmd_rcvrs_lock);
>  	synchronize_rcu();
>  
>  	list_for_each_entry_safe(rcvr, rcvr2, &list, link)
> @@ -812,7 +811,7 @@ int ipmi_destroy_user(ipmi_user_t user)
>  	 * since other things may be using it till we do
>  	 * synchronize_rcu()) then free everything in that list.
>  	 */
> -	spin_lock_irqsave(&intf->cmd_rcvrs_lock, flags);
> +	down(&intf->cmd_rcvrs_lock);
>  	list_for_each_safe_rcu(entry1, entry2, &intf->cmd_rcvrs) {
>  		rcvr = list_entry(entry1, struct cmd_rcvr, link);
>  		if (rcvr->user == user) {
> @@ -821,7 +820,7 @@ int ipmi_destroy_user(ipmi_user_t user)
>  			rcvrs = rcvr;
>  		}
>  	}
> -	spin_unlock_irqrestore(&intf->cmd_rcvrs_lock, flags);
> +	up(&intf->cmd_rcvrs_lock);
>  	synchronize_rcu();
>  	while (rcvrs) {
>  		rcvr = rcvrs;
> @@ -950,7 +949,7 @@ int ipmi_register_for_cmd(ipmi_user_t   
>  	rcvr->netfn = netfn;
>  	rcvr->user = user;
>  
> -	spin_lock_irq(&intf->cmd_rcvrs_lock);
> +	down(&intf->cmd_rcvrs_lock);
>  	/* Make sure the command/netfn is not already registered. */
>  	entry = find_cmd_rcvr(intf, netfn, cmd);
>  	if (entry) {
> @@ -961,7 +960,7 @@ int ipmi_register_for_cmd(ipmi_user_t   
>  	list_add_rcu(&rcvr->link, &intf->cmd_rcvrs);
>  
>   out_unlock:
> -	spin_unlock_irq(&intf->cmd_rcvrs_lock);
> +	up(&intf->cmd_rcvrs_lock);
>  	if (rv)
>  		kfree(rcvr);
>  
> @@ -975,17 +974,17 @@ int ipmi_unregister_for_cmd(ipmi_user_t 
>  	ipmi_smi_t      intf = user->intf;
>  	struct cmd_rcvr *rcvr;
>  
> -	spin_lock_irq(&intf->cmd_rcvrs_lock);
> +	down(&intf->cmd_rcvrs_lock);
>  	/* Make sure the command/netfn is not already registered. */
>  	rcvr = find_cmd_rcvr(intf, netfn, cmd);
>  	if ((rcvr) && (rcvr->user == user)) {
>  		list_del_rcu(&rcvr->link);
> -		spin_unlock_irq(&intf->cmd_rcvrs_lock);
> +		up(&intf->cmd_rcvrs_lock);
>  		synchronize_rcu();
>  		kfree(rcvr);
>  		return 0;
>  	} else {
> -		spin_unlock_irq(&intf->cmd_rcvrs_lock);
> +		up(&intf->cmd_rcvrs_lock);
>  		return -ENOENT;
>  	}
>  }
> @@ -1858,7 +1857,7 @@ int ipmi_register_smi(struct ipmi_smi_ha
>  	spin_lock_init(&intf->events_lock);
>  	INIT_LIST_HEAD(&intf->waiting_events);
>  	intf->waiting_events_count = 0;
> -	spin_lock_init(&intf->cmd_rcvrs_lock);
> +	init_MUTEX(&intf->cmd_rcvrs_lock);
>  	INIT_LIST_HEAD(&intf->cmd_rcvrs);
>  	init_waitqueue_head(&intf->waitq);
>  
> @@ -2058,14 +2057,14 @@ static int handle_ipmb_get_msg_cmd(ipmi_
>  	netfn = msg->rsp[4] >> 2;
>  	cmd = msg->rsp[8];
>  
> -	spin_lock_irqsave(&intf->cmd_rcvrs_lock, flags);
> +	rcu_read_lock();
>  	rcvr = find_cmd_rcvr(intf, netfn, cmd);
>  	if (rcvr) {
>  		user = rcvr->user;
>  		kref_get(&user->refcount);
>  	} else
>  		user = NULL;
> -	spin_unlock_irqrestore(&intf->cmd_rcvrs_lock, flags);
> +	rcu_read_unlock();
>  
>  	if (user == NULL) {
>  		/* We didn't find a user, deliver an error response. */
> @@ -2238,14 +2237,14 @@ static int handle_lan_get_msg_cmd(ipmi_s
>  	netfn = msg->rsp[6] >> 2;
>  	cmd = msg->rsp[10];
>  
> -	spin_lock_irqsave(&intf->cmd_rcvrs_lock, flags);
> +	rcu_read_lock();
>  	rcvr = find_cmd_rcvr(intf, netfn, cmd);
>  	if (rcvr) {
>  		user = rcvr->user;
>  		kref_get(&user->refcount);
>  	} else
>  		user = NULL;
> -	spin_unlock_irqrestore(&intf->cmd_rcvrs_lock, flags);
> +	rcu_read_unlock();
>  
>  	if (user == NULL) {
>  		/* We didn't find a user, just give up. */
>