From patchwork Wed Jul 5 23:31:35 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 784917 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 3x2xxR3Rwbz9s72 for ; Thu, 6 Jul 2017 09:32:43 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752811AbdGEXcD (ORCPT ); Wed, 5 Jul 2017 19:32:03 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:57002 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752633AbdGEXbu (ORCPT ); Wed, 5 Jul 2017 19:31:50 -0400 Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v65NSsIK030089 for ; Wed, 5 Jul 2017 19:31:50 -0400 Received: from e19.ny.us.ibm.com (e19.ny.us.ibm.com [129.33.205.209]) by mx0a-001b2d01.pphosted.com with ESMTP id 2bh3a6ym28-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 05 Jul 2017 19:31:49 -0400 Received: from localhost by e19.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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McKenney" To: linux-kernel@vger.kernel.org Cc: netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, oleg@redhat.com, akpm@linux-foundation.org, mingo@redhat.com, dave@stgolabs.net, manfred@colorfullife.com, tj@kernel.org, arnd@arndb.de, linux-arch@vger.kernel.org, will.deacon@arm.com, peterz@infradead.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, torvalds@linux-foundation.org, , Sasha Levin , Pablo Neira Ayuso , "Paul E. McKenney" Subject: [PATCH v2 1/9] net/netfilter/nf_conntrack_core: Fix net_conntrack_lock() Date: Wed, 5 Jul 2017 16:31:35 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170705232955.GA15992@linux.vnet.ibm.com> References: <20170705232955.GA15992@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17070523-0056-0000-0000-0000039EC411 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007326; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000214; SDB=6.00883401; UDB=6.00440697; IPR=6.00663592; BA=6.00005454; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00016100; XFM=3.00000015; UTC=2017-07-05 23:31:48 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17070523-0057-0000-0000-000007D4CA32 Message-Id: <1499297503-23852-1-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2017-07-05_16:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1707050383 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Manfred Spraul As we want to remove spin_unlock_wait() and replace it with explicit spin_lock()/spin_unlock() calls, we can use this to simplify the locking. In addition: - Reading nf_conntrack_locks_all needs ACQUIRE memory ordering. - The new code avoids the backwards loop. Only slightly tested, I did not manage to trigger calls to nf_conntrack_all_lock(). Fixes: b16c29191dc8 Signed-off-by: Manfred Spraul Cc: Cc: Sasha Levin Cc: Pablo Neira Ayuso Cc: netfilter-devel@vger.kernel.org Signed-off-by: Paul E. McKenney --- net/netfilter/nf_conntrack_core.c | 44 +++++++++++++++++++++------------------ 1 file changed, 24 insertions(+), 20 deletions(-) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index e847dbaa0c6b..1193565c38ae 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -96,19 +96,24 @@ static struct conntrack_gc_work conntrack_gc_work; void nf_conntrack_lock(spinlock_t *lock) __acquires(lock) { + /* 1) Acquire the lock */ spin_lock(lock); - while (unlikely(nf_conntrack_locks_all)) { - spin_unlock(lock); - /* - * Order the 'nf_conntrack_locks_all' load vs. the - * spin_unlock_wait() loads below, to ensure - * that 'nf_conntrack_locks_all_lock' is indeed held: - */ - smp_rmb(); /* spin_lock(&nf_conntrack_locks_all_lock) */ - spin_unlock_wait(&nf_conntrack_locks_all_lock); - spin_lock(lock); - } + /* 2) read nf_conntrack_locks_all, with ACQUIRE semantics */ + if (likely(smp_load_acquire(&nf_conntrack_locks_all) == false)) + return; + + /* fast path failed, unlock */ + spin_unlock(lock); + + /* Slow path 1) get global lock */ + spin_lock(&nf_conntrack_locks_all_lock); + + /* Slow path 2) get the lock we want */ + spin_lock(lock); + + /* Slow path 3) release the global lock */ + spin_unlock(&nf_conntrack_locks_all_lock); } EXPORT_SYMBOL_GPL(nf_conntrack_lock); @@ -149,18 +154,17 @@ static void nf_conntrack_all_lock(void) int i; spin_lock(&nf_conntrack_locks_all_lock); - nf_conntrack_locks_all = true; - /* - * Order the above store of 'nf_conntrack_locks_all' against - * the spin_unlock_wait() loads below, such that if - * nf_conntrack_lock() observes 'nf_conntrack_locks_all' - * we must observe nf_conntrack_locks[] held: - */ - smp_mb(); /* spin_lock(&nf_conntrack_locks_all_lock) */ + nf_conntrack_locks_all = true; for (i = 0; i < CONNTRACK_LOCKS; i++) { - spin_unlock_wait(&nf_conntrack_locks[i]); + spin_lock(&nf_conntrack_locks[i]); + + /* This spin_unlock provides the "release" to ensure that + * nf_conntrack_locks_all==true is visible to everyone that + * acquired spin_lock(&nf_conntrack_locks[]). + */ + spin_unlock(&nf_conntrack_locks[i]); } }