From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752572AbeEVQgI (ORCPT ); Tue, 22 May 2018 12:36:08 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:40314 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752424AbeEVQgD (ORCPT ); Tue, 22 May 2018 12:36:03 -0400 Date: Tue, 22 May 2018 09:36:48 -0700 From: "Paul E. McKenney" To: Roman Penyaev Cc: Linus Torvalds , linux-block , linux-rdma , Jens Axboe , Christoph Hellwig , Sagi Grimberg , Bart Van Assche , Or Gerlitz , Doug Ledford , "swapnil.ingle" , Danil Kipnis , Jinpu Wang , Linux Kernel Mailing List Subject: Re: [PATCH v2 01/26] rculist: introduce list_next_or_null_rr_rcu() Reply-To: paulmck@linux.vnet.ibm.com References: <20180518130413.16997-1-roman.penyaev@profitbricks.com> <20180518130413.16997-2-roman.penyaev@profitbricks.com> <20180519163735.GX3803@linux.vnet.ibm.com> <20180520004318.GY3803@linux.vnet.ibm.com> <20180521153337.GF3803@linux.vnet.ibm.com> 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-GCONF: 00 x-cbid: 18052216-0004-0000-0000-000014227E77 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009066; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000261; SDB=6.01036085; UDB=6.00529999; IPR=6.00815212; MB=3.00021242; MTD=3.00000008; XFM=3.00000015; UTC=2018-05-22 16:36:00 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18052216-0005-0000-0000-0000874F2A2D Message-Id: <20180522163648.GV3803@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-05-22_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1805220183 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 22, 2018 at 11:09:08AM +0200, Roman Penyaev wrote: > On Mon, May 21, 2018 at 5:33 PM, Paul E. McKenney > wrote: > > On Mon, May 21, 2018 at 08:16:59AM -0700, Linus Torvalds wrote: > >> On Mon, May 21, 2018 at 6:51 AM Roman Penyaev < > >> roman.penyaev@profitbricks.com> wrote: > >> > >> > No, I continue from the pointer, which I assigned on the previous IO > >> > in order to send IO fairly and keep load balanced. > >> > >> Right. And that's exactly what has both me and Paul nervous. You're no > >> longer in the RCU domain. You're using a pointer where the lifetime has > >> nothing to do with RCU any more. > >> > >> Can it be done? Sure. But you need *other* locking for it (that you haven't > >> explained), and it's fragile as hell. > > > > He looks to actually have it right, but I would want to see a big comment > > on the read side noting the leak of the pointer and documenting why it > > is OK. > > Hi Paul and Linus, > > Should I resend current patch with more clear comments about how careful > caller should be with a leaking pointer? Also I will update read side > with a fat comment about "rcu_assign_pointer()" which leaks the pointer > out of RCU domain and what is done to prevent nasty consequences. > Does that sound acceptable? That sounds good to me. Thanx, Paul