From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754909AbbE1Ujt (ORCPT ); Thu, 28 May 2015 16:39:49 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:39430 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754401AbbE1Ujn (ORCPT ); Thu, 28 May 2015 16:39:43 -0400 Date: Thu, 28 May 2015 13:39:38 -0700 From: josh@joshtriplett.org To: Dan Streetman Cc: Andrew Morton , "Paul E. McKenney" , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] rcu: introduce list_last_or_null_rcu Message-ID: <20150528203938.GA31076@cloud> References: <1432845328-27932-1-git-send-email-ddstreet@ieee.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1432845328-27932-1-git-send-email-ddstreet@ieee.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 28, 2015 at 04:35:27PM -0400, Dan Streetman wrote: > Add list_last_or_null_rcu(), to simplify getting the last entry from a > rcu-protected list. The standard list_last_entry() can't be used as it > is not rcu-protected; the list may be modified concurrently. And the > ->prev pointer can't be used, as only the ->next pointers are protected > by rcu. > > This simply iterates forward through the entire list, to get to the last > entry. If the list is empty, it returns NULL. > > Signed-off-by: Dan Streetman The list iteration functions are macros because they introduce a loop with attached loop block. For this, is there any reason not to make it an inline function instead of a macro? > include/linux/rculist.h | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/include/linux/rculist.h b/include/linux/rculist.h > index a18b16f..954fde5 100644 > --- a/include/linux/rculist.h > +++ b/include/linux/rculist.h > @@ -293,6 +293,27 @@ static inline void list_splice_init_rcu(struct list_head *list, > }) > > /** > + * list_last_or_null_rcu - get the last 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_head within the struct. > + * > + * Note that if the list is empty, it returns NULL. > + * > + * 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_last_or_null_rcu(ptr, type, member) \ > +({ \ > + struct list_head *__ptr = (ptr); \ > + struct list_head *__last = __ptr; \ > + struct list_head *__entry = list_next_rcu(__ptr); \ > + for (; __entry != __ptr; __entry = list_next_rcu(__entry)) \ > + __last = __entry; \ > + likely(__ptr != __last) ? list_entry_rcu(__last, type, member) : NULL; \ > +}) > + > +/** > * list_for_each_entry_rcu - iterate over rcu list of given type > * @pos: the type * to use as a loop cursor. > * @head: the head for your list. > -- > 2.1.0 >