From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752304AbdJFNgD (ORCPT ); Fri, 6 Oct 2017 09:36:03 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:59028 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752212AbdJFNel (ORCPT ); Fri, 6 Oct 2017 09:34:41 -0400 Date: Fri, 6 Oct 2017 06:34:36 -0700 From: "Paul E. McKenney" To: Paolo Abeni Cc: linux-kernel@vger.kernel.org, Josh Triplett , Steven Rostedt , "David S. Miller" , Eric Dumazet , Hannes Frederic Sowa , netdev@vger.kernel.org Subject: Re: [PATCH 0/4] RCU: introduce noref debug Reply-To: paulmck@linux.vnet.ibm.com References: 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: 17100613-0044-0000-0000-0000039B65A4 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007849; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000235; SDB=6.00927273; UDB=6.00466573; IPR=6.00707531; BA=6.00005623; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017420; XFM=3.00000015; UTC=2017-10-06 13:34:39 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17100613-0045-0000-0000-000007CA7634 Message-Id: <20171006133436.GY3521@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-06_04:,, 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=8.0.1-1707230000 definitions=main-1710060193 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 06, 2017 at 02:57:45PM +0200, Paolo Abeni wrote: > The networking subsystem is currently using some kind of long-lived > RCU-protected, references to avoid the overhead of full book-keeping. > > Such references - skb_dst() noref - are stored inside the skbs and can be > moved across relevant slices of the network stack, with the users > being in charge of properly clearing the relevant skb - or properly refcount > the related dst references - before the skb escapes the RCU section. > > We currently don't have any deterministic debug infrastructure to check > the dst noref usages - and the introduction of others noref artifact is > currently under discussion. > > This series tries to tackle the above introducing an RCU debug infrastructure > aimed at spotting incorrect noref pointer usage, in patch one. The > infrastructure is small and must be explicitly enabled via a newly introduced > build option. > > Patch two uses such infrastructure to track dst noref usage in the networking > stack. > > Patch 3 and 4 are bugfixes for small buglet found running this infrastructure > on basic scenarios. This patchset does not look like it handles rcu_read_lock() nesting. For example, given code like this: void foo(void) { rcu_read_lock(); rcu_track_noref(&key2, &noref2, true); do_something(); rcu_track_noref(&key2, &noref2, false); rcu_read_unlock(); } void bar(void) { rcu_read_lock(); rcu_track_noref(&key1, &noref1, true); do_something_more(); foo(); do_something_else(); rcu_track_noref(&key1, &noref1, false); rcu_read_unlock(); } void grill(void) { foo(); } It looks like foo()'s rcu_read_unlock() will complain about key1. You could remove foo()'s rcu_read_lock() and rcu_read_unlock(), but that will break the call from grill(). Or am I missing something subtle here? Given patch 3/4, I suspect not... Thanx, Paul > Paolo Abeni (4): > rcu: introduce noref debug > net: use RCU noref infrastructure to track dst noref > ipv4: drop unneeded and misleading RCU lock in ip_route_input_noref() > tcp: avoid noref dst leak on input path > > include/linux/rcupdate.h | 11 ++++++ > include/linux/skbuff.h | 1 + > include/net/dst.h | 5 +++ > kernel/rcu/Kconfig.debug | 15 ++++++++ > kernel/rcu/Makefile | 1 + > kernel/rcu/noref_debug.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++ > net/ipv4/route.c | 7 +--- > net/ipv4/tcp_input.c | 5 ++- > 8 files changed, 127 insertions(+), 7 deletions(-) > create mode 100644 kernel/rcu/noref_debug.c > > -- > 2.13.6 >