Re: [PATCH] Priority Lists for the RT mutex

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

On Thu, Apr 07, 2005 at 10:52:25AM -0700, Daniel Walker wrote:
> 
> Source: Daniel Walker <dwalker@mvista.com> MontaVista Software, Inc
> Description:
> 	This patch adds the priority list data structure from Inaky Perez-Gonzalez 
> to the Preempt Real-Time mutex.
> 
> the patch order is (starting with a 2.6.11 kernel tree),
> 
> patch-2.6.12-rc2
> realtime-preempt-2.6.12-rc2-V0.7.44-01
> 	
> Signed-off-by: Daniel Walker <dwalker@mvista.com>
> 
> Index: linux-2.6.11/include/linux/plist.h
> ===================================================================
> --- linux-2.6.11.orig/include/linux/plist.h	1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6.11/include/linux/plist.h	2005-04-07 17:47:42.000000000 +0000
> @@ -0,0 +1,310 @@

[ . . . ]

> +/* Grunt to do the real removal work of @pl from the plist. */
> +static inline
> +void __plist_del (struct plist *pl)
> +{
> +	struct list_head *victim;
> +	if (list_empty (&pl->dp_node))  	/* SP-node, not head */
> +		victim = &pl->sp_node;
> +	else if (list_empty (&pl->sp_node)) 	/* DP-node, empty SP list */
> +		victim = &pl->dp_node;
> +	else {					/* SP list head, not empty */
> +		struct plist *pl_new = container_of (pl->sp_node.next,
> +						     struct plist, sp_node);
> +		victim = &pl->sp_node;
> +		list_replace_rcu (&pl->dp_node, &pl_new->dp_node);

If you are protecting this list with RCU...

> +	}
> +	list_del_init (victim);

... you need to wait for a grace period before deleting the element
removed from the list.

Or are you just using list_replace_rcu() for its replacement capability?
If so, seems like it might be worthwhile to make a list_replace().
This would get rid of the memory barrier, and also keep from confusing
people like myself.  ;-)

							Thanx, Paul