From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754806AbbE1VGL (ORCPT ); Thu, 28 May 2015 17:06:11 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:57743 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754306AbbE1VFv (ORCPT ); Thu, 28 May 2015 17:05:51 -0400 Date: Thu, 28 May 2015 14:05:46 -0700 From: "Paul E. McKenney" To: Dan Streetman Cc: josh@joshtriplett.org, Andrew Morton , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , linux-kernel Subject: Re: [PATCH 1/2] rcu: introduce list_last_or_null_rcu Message-ID: <20150528210546.GM5989@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1432845328-27932-1-git-send-email-ddstreet@ieee.org> <20150528203938.GA31076@cloud> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15052821-0021-0000-0000-00000AEDD11D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 28, 2015 at 04:42:20PM -0400, Dan Streetman wrote: > On Thu, May 28, 2015 at 4:39 PM, wrote: > > 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? > > true, there's no reason i can see not to make it inline, let me send > an updated patch. Hmmm... If we can now do type-generic inline functions, it might make sense to convert some of the others as well. Thanx, Paul > >> 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 > >> >