From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755932AbdEDQzf (ORCPT ); Thu, 4 May 2017 12:55:35 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:34212 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751468AbdEDQz2 (ORCPT ); Thu, 4 May 2017 12:55:28 -0400 Date: Thu, 4 May 2017 09:55:21 -0700 From: "Paul E. McKenney" To: Petr Mladek Cc: Josh Poimboeuf , Jessica Yu , Jiri Kosina , Miroslav Benes , Steven Rostedt , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/3] livepatch/rcu: Handle some subtle issues between livepatching and RCU Reply-To: paulmck@linux.vnet.ibm.com References: <1493895316-19165-1-git-send-email-pmladek@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1493895316-19165-1-git-send-email-pmladek@suse.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17050416-0052-0000-0000-000001F313EF X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007021; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000209; SDB=6.00856213; UDB=6.00423836; IPR=6.00635377; BA=6.00005326; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015306; XFM=3.00000014; UTC=2017-05-04 16:55:25 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17050416-0053-0000-0000-0000507125D2 Message-Id: <20170504165521.GA3956@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-04_11:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1705040255 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 04, 2017 at 12:55:13PM +0200, Petr Mladek wrote: > Steven and Paul recently discussed some issues when using RCU > functionality in ftrace handlers. A good summary can be found at > https://lkml.kernel.org/r/20170412115304.3077dbc8@gandalf.local.home > > This discussion made us to revisit the ftrace handler used by > the livepatches. Some changes seem to be needed. A perfect solution > looks rather complicated. I have implemented a sub-optimal > one and split it into three patches for easier review. > > Please, note that we were on the safe side before introducing > the hybrid consistency model. The ftrace handler worked correctly > with empty function stack. Also the patch removal was not possible. > But we need to be more careful now. I don't know enough to say much about the live patching, but the characterization of how RCU works is correct. Thanx, Paul > Petr Mladek (3): > livepatch/rcu: Guarantee consistency when patching idle kthreads > livepatch/rcu: Warn when system consistency is broken in RCU code > livepatch/rcu: Disable livepatch removal when safety is not guaranteed > > Documentation/livepatch/livepatch.txt | 19 +++++++++++++++++++ > kernel/livepatch/patch.c | 14 ++++++++++++++ > kernel/livepatch/transition.c | 7 ++++++- > kernel/livepatch/transition.h | 2 ++ > 4 files changed, 41 insertions(+), 1 deletion(-) > > -- > 1.8.5.6 >