linux-kernel - Re: [PATCH] rculist.h: introduce list_entry_rcu and list_first_entry

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Date:	Tue, 14 Apr 2009 08:53:27 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	linux-kernel@...r.kernel.org, dipankar@...ibm.com, mingo@...e.hu
Subject: Re: [PATCH] rculist.h: introduce list_entry_rcu and
	list_first_entry_rcu

On Tue, Apr 14, 2009 at 05:33:57PM +0200, Jiri Pirko wrote:
> I've run into the situation where I need to use list_first_entry with
> rcu-guarded list. This patch introduces this. Also changed
> list_for_each_entry_rcu to use new list_entry_rcu instead of list_entry.
> 
> Jirka

Looks good -- and very nice list_entry_rcu() primitive!

There are a couple more places where this primitive could be applied.
I would welcome a patch for these as well.

include/linux/sched.h next_task 1986 #define next_task(p) list_entry(rcu_dereference((p)->tasks.next), struct task_struct, tasks)
include/linux/sched.h next_thread 2025 return list_entry(rcu_dereference(p->thread_group.next),
ipc/sem.c exit_sem 1293 un = list_entry(rcu_dereference(ulp->list_proc.next),

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> Signed-off-by: Jiri Pirko <jpirko@...hat.com>
> ---
>  include/linux/rculist.h |   30 ++++++++++++++++++++++++++++--
>  1 files changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index e649bd3..5710f43 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -198,6 +198,32 @@ static inline void list_splice_init_rcu(struct list_head *list,
>  	at->prev = last;
>  }
> 
> +/**
> + * list_entry_rcu - get the struct for this entry
> + * @ptr:        the &struct list_head pointer.
> + * @type:       the type of the struct this is embedded in.
> + * @member:     the name of the list_struct within the struct.
> + *
> + * This primitive may safely run concurrently with the _rcu list-mutation
> + * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
> + */
> +#define list_entry_rcu(ptr, type, member) \
> +	container_of(rcu_dereference(ptr), type, member)
> +
> +/**
> + * list_first_entry_rcu - get the first element from a list
> + * @ptr:        the list head to take the element from.
> + * @type:       the type of the struct this is embedded in.
> + * @member:     the name of the list_struct within the struct.
> + *
> + * Note, that list is expected to be not empty.
> + *
> + * This primitive may safely run concurrently with the _rcu list-mutation
> + * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
> + */
> +#define list_first_entry_rcu(ptr, type, member) \
> +	list_entry_rcu((ptr)->next, type, member)
> +
>  #define __list_for_each_rcu(pos, head) \
>  	for (pos = rcu_dereference((head)->next); \
>  		pos != (head); \
> @@ -214,9 +240,9 @@ static inline void list_splice_init_rcu(struct list_head *list,
>   * as long as the traversal is guarded by rcu_read_lock().
>   */
>  #define list_for_each_entry_rcu(pos, head, member) \
> -	for (pos = list_entry(rcu_dereference((head)->next), typeof(*pos), member); \
> +	for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
>  		prefetch(pos->member.next), &pos->member != (head); \
> -		pos = list_entry(rcu_dereference(pos->member.next), typeof(*pos), member))
> +		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
> 
> 
>  /**
> -- 
> 1.6.0.6
> 
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