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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 171B3C001DC for ; Fri, 21 Jul 2023 15:59:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231995AbjGUP74 (ORCPT ); Fri, 21 Jul 2023 11:59:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59500 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232336AbjGUP7s (ORCPT ); Fri, 21 Jul 2023 11:59:48 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C4101359D for ; Fri, 21 Jul 2023 08:59:42 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with both STARTTLS and AUTH (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-255-XYwML9_NPc6-LFPMycNl4g-1; Fri, 21 Jul 2023 16:59:40 +0100 X-MC-Unique: XYwML9_NPc6-LFPMycNl4g-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Fri, 21 Jul 2023 16:59:39 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Fri, 21 Jul 2023 16:59:38 +0100 From: David Laight To: 'Joel Fernandes' , Alan Huang CC: Eric Dumazet , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "rcu@vger.kernel.org" , "Paul E. McKenney" , "roman.gushchin@linux.dev" Subject: RE: Question about the barrier() in hlist_nulls_for_each_entry_rcu() Thread-Topic: Question about the barrier() in hlist_nulls_for_each_entry_rcu() Thread-Index: AQHZu+cDW9UBwZmf30GL9p6MGC4yBq/EWe3Q Date: Fri, 21 Jul 2023 15:59:38 +0000 Message-ID: <962bb2b940e64e7da7b71d11b307defc@AcuMS.aculab.com> References: <1E0741E0-2BD9-4FA3-BA41-4E83315A10A8@joelfernandes.org> <1AF98387-B78C-4556-BE2E-E8F88ADACF8A@gmail.com> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: base64 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Li4uLg0KPiBSaWdodCwgaXQgc2hvdWxkbid0IG5lZWQgdG8gY2FjaGUuIFRvIEVyaWMncyBwb2lu dCBpdCBtaWdodCBiZSByaXNreSB0byByZW1vdmUNCj4gdGhlIGJhcnJpZXIoKSBhbmQgc29tZW9u ZSBuZWVkcyB0byBleHBsYWluIHRoYXQgaXNzdWUgZmlyc3QgKG9yIElNTyB0aGVyZSBuZWVkcw0K PiB0byBiZSBhbm90aGVyIHRhbmdpYmxlIHJlYXNvbiBsaWtlIHBlcmZvcm1hbmNlIGV0YykuIEFu eXdheSwgRldJVyBJIHdyb3RlIGENCj4gc2ltcGxlIHByb2dyYW0gYW5kIEkgYW0gbm90IHNlZWlu ZyB0aGUgaGVhZC0+Zmlyc3QgY2FjaGVkIHdpdGggdGhlIHBhdHRlcm4geW91DQo+IHNoYXJlZCBh Ym92ZToNCj4gDQo+ICNpbmNsdWRlIDxzdGRsaWIuaD4NCj4gDQo+ICNkZWZpbmUgUkVBRF9PTkNF KHgpICgqKHZvbGF0aWxlIHR5cGVvZih4KSAqKSYoeCkpDQo+ICNkZWZpbmUgYmFycmllcigpIF9f YXNtX18gX192b2xhdGlsZV9fKCIiOiA6IDoibWVtb3J5IikNCj4gDQo+IHR5cGVkZWYgc3RydWN0 IGxpc3RfaGVhZCB7DQo+ICAgICAgaW50IGZpcnN0Ow0KPiAgICAgIHN0cnVjdCBsaXN0X2hlYWQg Km5leHQ7DQo+IH0gbGlzdF9oZWFkOw0KPiANCj4gaW50IG1haW4oKSB7DQo+ICAgICAgbGlzdF9o ZWFkICpoZWFkID0gKGxpc3RfaGVhZCAqKW1hbGxvYyhzaXplb2YobGlzdF9oZWFkKSk7DQo+ICAg ICAgaGVhZC0+Zmlyc3QgPSAxOw0KPiAgICAgIGhlYWQtPm5leHQgPSAwOw0KPiANCj4gICAgICBS RUFEX09OQ0UoaGVhZC0+Zmlyc3QpOw0KPiAgICAgIGJhcnJpZXIoKTsNCj4gICAgICBSRUFEX09O Q0UoaGVhZC0+Zmlyc3QpOw0KPiANCj4gICAgICBmcmVlKGhlYWQpOw0KPiAgICAgIHJldHVybiAw Ow0KPiB9DQoNCllvdSBwcm9iYWJseSBuZWVkIHRvIHRyeSBoYXJkZXIgdG8gZ2VuZXJhdGUgdGhl IGVycm9yLg0KSXQgcHJvYmFibHkgaGFzIHNvbWV0aGluZyB0byBkbyBjb2RlIHN1cnJvdW5kaW5n IHRoZQ0Kc2tfbnVsbHNfZm9yX2VhY2hfcmN1KCkgaW4gdGhlIGNhMDY1ZDBjXiB2ZXJzaW9uIG9m IHVkcC5jLg0KDQpUaGF0IHBhdGNoIHJlbW92ZXMgdGhlIHJldHJ5IGxvb3AgLSBhbmQgcHJvYmFi bHkgYnJlYWtzIHVkcCByZWNlaXZlLg0KVGhlIGlzc3VlIGlzIHRoYXQgc29ja2V0cyBjYW4gYmUg bW92ZWQgYmV0d2VlbiB0aGUgJ2hhc2gyJyBjaGFpbnMNCihlZyBieSBjb25uZWN0KCkpIHdpdGhv dXQgYmVpbmcgZnJlZWQuDQoNCglEYXZpZA0KDQotDQpSZWdpc3RlcmVkIEFkZHJlc3MgTGFrZXNp ZGUsIEJyYW1sZXkgUm9hZCwgTW91bnQgRmFybSwgTWlsdG9uIEtleW5lcywgTUsxIDFQVCwgVUsN ClJlZ2lzdHJhdGlvbiBObzogMTM5NzM4NiAoV2FsZXMpDQo=