From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4ACA0C43381 for ; Tue, 26 Mar 2019 15:36:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 20CE42075C for ; Tue, 26 Mar 2019 15:36:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731988AbfCZPg5 (ORCPT ); Tue, 26 Mar 2019 11:36:57 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34748 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726285AbfCZPgy (ORCPT ); Tue, 26 Mar 2019 11:36:54 -0400 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x2QFUnek087959 for ; Tue, 26 Mar 2019 11:36:52 -0400 Received: from e13.ny.us.ibm.com (e13.ny.us.ibm.com [129.33.205.203]) by mx0a-001b2d01.pphosted.com with ESMTP id 2rfpf89jft-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 26 Mar 2019 11:36:52 -0400 Received: from localhost by e13.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 26 Mar 2019 15:36:48 -0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22035.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x2QFakCp17235984 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 26 Mar 2019 15:36:47 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 66FECB2071; Tue, 26 Mar 2019 15:36:46 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 49C6CB2064; Tue, 26 Mar 2019 15:36:46 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.188]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Tue, 26 Mar 2019 15:36:46 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id CB18016C3238; Tue, 26 Mar 2019 08:36:46 -0700 (PDT) Date: Tue, 26 Mar 2019 08:36:46 -0700 From: "Paul E. McKenney" To: Herbert Xu Cc: NeilBrown , Thomas Graf , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/4] rhashtable: use bit_spin_locks to protect hash bucket. Reply-To: paulmck@linux.ibm.com References: <155349021177.1111.15681654355431465791.stgit@noble.brown> <155349033961.1111.18247269615646768227.stgit@noble.brown> <20190326050320.gwk3tgtqwl5csivt@gondor.apana.org.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190326050320.gwk3tgtqwl5csivt@gondor.apana.org.au> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19032615-0064-0000-0000-000003C04506 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010818; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000282; SDB=6.01179981; UDB=6.00617481; IPR=6.00960696; MB=3.00026164; MTD=3.00000008; XFM=3.00000015; UTC=2019-03-26 15:36:50 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19032615-0065-0000-0000-00003CD7D1CA Message-Id: <20190326153646.GL4102@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-03-26_11:,, 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 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903260108 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Mar 26, 2019 at 01:03:20PM +0800, Herbert Xu wrote: > On Mon, Mar 25, 2019 at 04:05:39PM +1100, NeilBrown wrote: > > > > + * Sometimes we unlock a bucket by writing a new pointer there. In that > > + * case we don't need to unlock, but we do need to reset state such as > > + * local_bh. For that we have rht_unlocked(). This doesn't include > > + * the memory barrier that bit_spin_unlock() provides, but rcu_assign_pointer() > > + * will have provided that. > > Hmm, are you sure that's enough? IIRC rcu_assign_pointer only > provides a write barrier compared to the more complete (but one-way) > barrier that a spin-lock provides. Not seeing the code, I have no opinion on the safety in this case, but I did want to mention that rcu_assign_pointer() has been upgraded to a release store, so that it orders all prior accesses from the viewpoint of some other thread that just picked up the stored pointer via rcu_dereference(). But you are quite right, rcu_assign_pointer() used to just do an smp_wmb(). It is now new and improved! ;-) Thanx, Paul