From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754482AbbJ1Ufs (ORCPT ); Wed, 28 Oct 2015 16:35:48 -0400 Received: from mail-wi0-f173.google.com ([209.85.212.173]:35475 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751182AbbJ1Ufq (ORCPT ); Wed, 28 Oct 2015 16:35:46 -0400 Subject: Re: [PATCH tip/core/rcu 11/13] rculist: Make list_entry_rcu() use lockless_dereference() To: Ingo Molnar , Tejun Heo References: <20151006161305.GA9799@linux.vnet.ibm.com> <1444148028-11551-1-git-send-email-paulmck@linux.vnet.ibm.com> <1444148028-11551-11-git-send-email-paulmck@linux.vnet.ibm.com> <20151026084506.GA28423@gmail.com> <20151026145552.GG5105@linux.vnet.ibm.com> <20151027051939.GA19355@mtj.duckdns.org> <20151028083353.GA824@gmail.com> Cc: Linus Torvalds , Paul McKenney , Linux Kernel Mailing List , Lai Jiangshan , Dipankar Sarma , Andrew Morton , Mathieu Desnoyers , Josh Triplett , Thomas Gleixner , Peter Zijlstra , Steven Rostedt , David Howells , Eric Dumazet , Darren Hart , =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= , Oleg Nesterov , pranith kumar From: Patrick Marlier Message-ID: <5631319E.5000606@gmail.com> Date: Wed, 28 Oct 2015 21:35:42 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151028083353.GA824@gmail.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/28/2015 09:33 AM, Ingo Molnar wrote: > > * Tejun Heo wrote: > >> Subject: writeback: don't use list_entry_rcu() for pointer offsetting in bdi_split_work_to_wbs() >> >> bdi_split_work_to_wbs() uses list_for_each_entry_rcu_continue() to >> walk @bdi->wb_list. To set up the initial iteration condition, it >> uses list_entry_rcu() to calculate the entry pointer corresponding to >> the list head; however, this isn't an actual RCU dereference and using >> list_entry_rcu() for it ended up breaking a proposed list_entry_rcu() >> change because it was feeding an non-lvalue pointer into the macro. >> >> Don't use the RCU variant for simple pointer offsetting. Use >> list_entry() instead. >> >> Signed-off-by: Tejun Heo >> --- >> fs/fs-writeback.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c >> index 29e4599..7378169 100644 >> --- a/fs/fs-writeback.c >> +++ b/fs/fs-writeback.c >> @@ -779,8 +779,8 @@ static void bdi_split_work_to_wbs(struct backing_dev_info *bdi, >> bool skip_if_busy) >> { >> struct bdi_writeback *last_wb = NULL; >> - struct bdi_writeback *wb = list_entry_rcu(&bdi->wb_list, >> - struct bdi_writeback, bdi_node); >> + struct bdi_writeback *wb = list_entry(&bdi->wb_list, >> + struct bdi_writeback, bdi_node); >> >> might_sleep(); > > Any objections against me applying this fix to tip:core/rcu so that I can push the > recent RCU changes towards linux-next without triggering a build failure? No objection on my side but probably you are waiting for an ack from somebody else. -- Pat