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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Nov 2022 16:56:02.4696 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 44e847e1-fa92-4313-f8ca-08dacbe145d3 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: VI1EUR03FT031.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB6181 X-Spam-Status: No, score=-5.6 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,KAM_DMARC_NONE,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP,UNPARSEABLE_RELAY autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Hi Florian,=0A= =0A= >> Fix memory ordering issues in the fastbin implementation: in REMOVE_FB t= he=0A= >> next pointer is read before any MO synchronization, however in the C11 a= tomic=0A= >> model this is only correct after a load acquire. Refactor the fastbin co= de=0A= >> and add a dedicated fastbin_push/pop implementation. The number of acqui= re=0A= >> or release atomics remains the same, and the new functions are inlined, = so=0A= >> performance is unaffected.=0A= >>=0A= >> Passes regress, OK for commit?=0A= >=0A= > Did you actually observe any problems resulting from this?=A0 We=0A= > previously concluded that the dependency chain would mae this valid=0A= > (outside the C11 memory model).=0A= =0A= No, I believe it works in most weak memory models (except for Alpha).=0A= However the code always looked weird with the acquire done after several=0A= non-atomic accesses... The key is that we need to do the acquire/release=0A= only once per iteration in the CAS loop, and that avoids regressions.=0A= =0A= Cheers,=0A= Wilco= From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from EUR01-DB5-obe.outbound.protection.outlook.com (mail-eopbgr150075.outbound.protection.outlook.com [40.107.15.75]) by sourceware.org (Postfix) with ESMTPS id 7D105384F6FD for ; Mon, 21 Nov 2022 16:56:26 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 7D105384F6FD Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=arm.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=armh.onmicrosoft.com; s=selector2-armh-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=hQZuVgACnNGq2Whr8dbt4QcSko4OW9YlVyVI/FHjdTw=; b=Y3rXKdxeoWkcepKmuRcz2Fc1GSKIWgKH8jPpgJ6k9zRTS1dwSQaYgSZ3A+hEW3oiU6hhycPAZks5rGscaxcRU55r6CF4sKaRq8Kpu//Nkj4lq2pN1LCsKWdfJVNIjB/RpHMIEPOIaPc3YjtSXAxmtSuAWMmcrw7sd74dkQB419k= Received: from DUZPR01CA0050.eurprd01.prod.exchangelabs.com (2603:10a6:10:469::20) by DBBPR08MB6185.eurprd08.prod.outlook.com (2603:10a6:10:207::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.5857.17; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Nov 2022 16:56:21.6071 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 9effa358-c19e-4aa6-6f04-08dacbe1512b X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: DBAEUR03FT036.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DBBPR08MB6185 X-Spam-Status: No, score=-5.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,FORGED_SPF_HELO,KAM_DMARC_NONE,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,TXREP,UNPARSEABLE_RELAY autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Message-ID: <20221121165619.1XXGdv8oIMATy51qKHfqUYmCR9UrXl9aQl_hyjOnvAk@z> Hi Florian,=0A= =0A= >> Fix memory ordering issues in the fastbin implementation: in REMOVE_FB t= he=0A= >> next pointer is read before any MO synchronization, however in the C11 a= tomic=0A= >> model this is only correct after a load acquire. Refactor the fastbin co= de=0A= >> and add a dedicated fastbin_push/pop implementation. The number of acqui= re=0A= >> or release atomics remains the same, and the new functions are inlined, = so=0A= >> performance is unaffected.=0A= >>=0A= >> Passes regress, OK for commit?=0A= >=0A= > Did you actually observe any problems resulting from this?=A0 We=0A= > previously concluded that the dependency chain would mae this valid=0A= > (outside the C11 memory model).=0A= =0A= No, I believe it works in most weak memory models (except for Alpha).=0A= However the code always looked weird with the acquire done after several=0A= non-atomic accesses... The key is that we need to do the acquire/release=0A= only once per iteration in the CAS loop, and that avoids regressions.=0A= =0A= Cheers,=0A= Wilco=