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 6D2FCEB64DA for ; Sat, 22 Jul 2023 14:06:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229614AbjGVOGz (ORCPT ); Sat, 22 Jul 2023 10:06:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60372 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229597AbjGVOGy (ORCPT ); Sat, 22 Jul 2023 10:06:54 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3FCEC2D7B for ; Sat, 22 Jul 2023 07:06:51 -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-122-J7OFbQsWNqyfCrR826JB4A-1; Sat, 22 Jul 2023 15:06:48 +0100 X-MC-Unique: J7OFbQsWNqyfCrR826JB4A-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; Sat, 22 Jul 2023 15:06:47 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Sat, 22 Jul 2023 15:06:47 +0100 From: David Laight To: 'Alan Huang' , Joel Fernandes , "Paul E. McKenney" , "Eric Dumazet" , "roman.gushchin@linux.dev" CC: "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "rcu@vger.kernel.org" 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: AQHZvKDlW9UBwZmf30GL9p6MGC4yBq/F0Gvg Date: Sat, 22 Jul 2023 14:06:47 +0000 Message-ID: <8e1885b62d124cca9198ff6cdb52c7f5@AcuMS.aculab.com> References: <1E0741E0-2BD9-4FA3-BA41-4E83315A10A8@joelfernandes.org> <1AF98387-B78C-4556-BE2E-E8F88ADACF8A@gmail.com> <76552616-5DF1-4A05-BA5A-AE0677F861FC@gmail.com> In-Reply-To: <76552616-5DF1-4A05-BA5A-AE0677F861FC@gmail.com> 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: rcu@vger.kernel.org Li4uLg0KPiA+IEZvdW5kIGEgcmVsYXRlZCBkaXNjdXNzaW9uOg0KPiA+DQo+ID4gaHR0cHM6Ly9n Y2MuZ251Lm9yZy9idWd6aWxsYS9zaG93X2J1Zy5jZ2k/aWQ9MTAyNzE0DQo+ID4NCj4gPiBMb29r cyBsaWtlIEdDQyAxMCwgMTEgaGF2ZSBiZWVuIGJhY2twb3J0ZWQsIG5vdCBzdXJlIHdoZXRoZXIg R0NDIDggaGFzIGJlZW4gYmFja3BvcnRlZC4NCj4gPg0KPiA+IFNvLCBJIGhhdmUgdGhlIGZvbGxv d2luZyBxdWVzdGlvbnM6DQo+ID4NCj4gPiBHaXZlbiB0aGF0IHNvbWUgcGVvcGxlIG1pZ2h0IG5v dCB1cGRhdGUgdGhlaXIgR0NDLCBkbyB0aGV5IG5lZWQgdG8gYmUgbm90aWZpZWQ/DQo+ID4NCj4g PiBEbyB3ZSBuZWVkIHRvIENDIExpbnVzPw0KPiANCj4gTm8gbmVlZC4NCj4gDQo+IEkgcHV0IHRo ZSBmb2xsb3dpbmcgY29kZSBpbnRvIGEga2VybmVsIG1vZHVsZToNCj4gDQo+IHR5cGVkZWYgc3Ry dWN0IGxpc3RfaGVhZF9zaGl0IHsNCj4gCWludCBuZXh0Ow0KPiAJc3RydWN0IGxpc3RfaGVhZCAq Zmlyc3Q7DQo+IH0gbGlzdF9oZWFkX3NoaXQ7DQo+IA0KPiBzdGF0aWMgdm9pZCBub2lubGluZSBz b19zaGl0KHZvaWQpIHsNCj4gCWxpc3RfaGVhZF9zaGl0ICpoZWFkID0gKGxpc3RfaGVhZF9zaGl0 ICopa21hbGxvYyhzaXplb2YobGlzdF9oZWFkX3NoaXQpLCBHRlBfS0VSTkVMKTsNCj4gCWhlYWQt PmZpcnN0ID0gMDsNCj4gCWhlYWQtPm5leHQgPSAxOw0KPiANCj4gCVJFQURfT05DRShoZWFkLT5m aXJzdCk7DQo+IAlSRUFEX09OQ0UoaGVhZC0+Zmlyc3QpOw0KPiANCj4gCWtmcmVlKGhlYWQpOw0K PiB9DQo+IA0KPiB4ODZfNjQtbGludXgtZ251LWdjYy0xMSBnZW5lcmF0ZSB0aGUgZm9sbG93aW5n IGNvZGU6DQo+IA0KPiAwMDAwMDAwMDAwMDAwMDAwIDxzb19zaGl0PjoNCj4gICAgMDoJNDggOGIg M2QgMDAgMDAgMDAgMDAgCW1vdiAgICAweDAoJXJpcCksJXJkaSAgICAgICAgIyA3IDxzb19zaGl0 KzB4Nz4NCj4gICAgNzoJYmEgMTAgMDAgMDAgMDAgICAgICAgCQltb3YgICAgJDB4MTAsJWVkeA0K PiAgICBjOgliZSBjMCAwYyAwMCAwMCAgICAgIAkgCW1vdiAgICAkMHhjYzAsJWVzaQ0KPiAgIDEx OgllOCAwMCAwMCAwMCAwMCAgICAgIAkgCWNhbGwgICAxNiA8c29fc2hpdCsweDE2Pg0KPiAgIDE2 Ogk0OCBjNyA0MCAwOCAwMCAwMCAwMCAJbW92cSAgICQweDAsMHg4KCVyYXgpDQo+ICAgMWQ6CTAw DQo+ICAgMWU6CTQ4IDg5IGM3ICAgICAgICAgICAgIAkJbW92ICAgICVyYXgsJXJkaQ0KPiAgIDIx OgljNyAwMCAwMSAwMCAwMCAwMCAgICAJbW92bCAgICQweDEsKCVyYXgpDQo+ICAgMjc6CTQ4IDhi IDQ3IDA4ICAgICAgICAgIAkJbW92ICAgIDB4OCglcmRpKSwlcmF4CSAgIyBSRUFEX09OQ0UgaGVy ZQ0KPiAgIDJiOgk0OCA4YiA0NyAwOCAgICAgICAgICAJCW1vdiAgICAweDgoJXJkaSksJXJheAkg ICMgUkVBRF9PTkNFIGhlcmUNCj4gICAyZjoJZTkgMDAgMDAgMDAgMDAgICAgICAJIAlqbXAgICAg MzQgPHNvX3NoaXQrMHgzND4NCj4gICAzNDoJNjYgNjYgMmUgMGYgMWYgODQgMDAgCWRhdGExNiBj cyBub3B3IDB4MCglcmF4LCVyYXgsMSkNCj4gICAzYjoJMDAgMDAgMDAgMDANCj4gICAzZjoJOTAg ICAgICAgICAgICAgICAgICAgCQkJbm9wDQo+IA0KPiBUaGUgY29uY2x1c2lvbiBpcyB0aGF0IHdl IGNhbiByZWx5IG9uIFJFQURfT05DRSB3aGVuIHdyaXRpbmcga2VybmVsIGNvZGUuDQo+IA0KPiBU aGUga2VybmVs4oCZcyBSRUFEX09OQ0UgaXMgZGlmZmVyZW50IHdpdGggdGhlIG9uZSBKb2VsIHdy b3RlIHllc3RlcmRheS4gKEpvZWzigJlzIGlzIHRoZSBzYW1lIGFzIHRoZSBvbGQNCj4gQUNDRVNT X09OQ0UpDQoNCllvdSBkbyBuZWVkIHRvIHJlcHJvZHVjZSB0aGUgZXJyb3Igd2l0aCBjb2RlIHRo YXQgbG9va3MgbGlrZQ0KdGhlIGxvb3AgaW4gdGhlIChvbGQpIHVkcC5jIGNvZGUuDQoNClRoZW4g c2VlIGlmIGNoYW5naW5nIHRoZSBpbXBsZW1lbnRhdGlvbiBvZiBSRUFEX09OQ0UoKSBmcm9tDQph IHNpbXBsZSAndm9sYXRpbGUnIGFjY2VzcyB0aGUgbmV3ZXIgdmFyaWFudCBtYWtlcyBhIGRpZmZl cmVuY2UuDQoNCllvdSBhbHNvIG5lZWQgdG8gY2hlY2sgd2l0aCB0aGUgb2xkZXN0IHZlcnNpb24g b2YgZ2NjIHRoYXQgaXMNCnN0aWxsIHN1cHBvcnRlZCAtIHRoYXQgaXMgbXVjaCBvbGRlciB0aGFu IGdjYyAxMS4NCg0KSW4gdGhlIHVkcCBjb2RlIHRoZSB2b2xhdGlsZSBhY2Nlc3Mgd2FzIG9uIGEg cG9pbnRlciAod2hpY2ggc2hvdWxkDQpxdWFsaWZ5IGFzIGEgc2NhbGVyIHR5cGUpIHNvIGl0IG1h eSB3ZWxsIGJlIHRoZSBpbmxpbmluZyBidWcgeW91DQptZW50aW9uZWQgZWFybGllciwgbm90IHRo ZSAndm9sYXRpbGUgb24gbm9uLXNjYWxlcicgZmVhdHVyZSB0aGF0DQpSRUFEX09OQ0UoKSBmaXhl ZC4NClRoYXQgZml4IGhhc24ndCBiZWVuIGJhY2stcG9ydGVkIHRvIGFsbCB0aGUgdmVyc2lvbnMg b2YgZ2NjDQp0aGF0IHRoZSBrZXJuZWwgYnVpbGQgc3VwcG9ydHMuDQoNCglEYXZpZA0KDQotDQpS ZWdpc3RlcmVkIEFkZHJlc3MgTGFrZXNpZGUsIEJyYW1sZXkgUm9hZCwgTW91bnQgRmFybSwgTWls dG9uIEtleW5lcywgTUsxIDFQVCwgVUsNClJlZ2lzdHJhdGlvbiBObzogMTM5NzM4NiAoV2FsZXMp DQo=