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Thu, 1 Sep 2022 14:19:24 +0000 From: Wilco Dijkstra To: Adhemerval Zanella Netto CC: 'GNU C Library' Subject: Re: [PATCH] elf: Use C11 like atomics on _dl_mcount Thread-Topic: [PATCH] elf: Use C11 like atomics on _dl_mcount Thread-Index: AQHYvfovPDBwefSqqEe296UxU2qQoq3KjBSAgAADjYM= Date: Thu, 1 Sep 2022 14:19:24 +0000 Message-ID: References: <59b9367c-08f1-4f38-7273-b5eca48be60e@linaro.org> In-Reply-To: <59b9367c-08f1-4f38-7273-b5eca48be60e@linaro.org> Accept-Language: en-GB, en-US Content-Language: en-GB X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: Authentication-Results-Original: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=arm.com; X-MS-Office365-Filtering-Correlation-Id: 27d0c0cd-f1b0-4670-4f99-08da8c24fe1d x-ms-traffictypediagnostic: AM0PR08MB5329:EE_|AM7EUR03FT043:EE_|DB9PR08MB6457:EE_ x-checkrecipientrouted: true nodisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0; X-Microsoft-Antispam-Message-Info-Original: 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 X-Forefront-Antispam-Report-Untrusted: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:AS4PR08MB7901.eurprd08.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230016)(4636009)(366004)(396003)(136003)(346002)(376002)(39860400002)(8936002)(76116006)(478600001)(66556008)(8676002)(66476007)(66446008)(66946007)(52536014)(64756008)(5660300002)(83380400001)(4326008)(41300700001)(38070700005)(33656002)(26005)(9686003)(91956017)(4744005)(71200400001)(186003)(7696005)(38100700002)(122000001)(6506007)(316002)(55016003)(6916009)(2906002)(86362001);DIR:OUT;SFP:1101; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Sep 2022 14:19:33.5922 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 27d0c0cd-f1b0-4670-4f99-08da8c24fe1d 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: AM7EUR03FT043.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB9PR08MB6457 X-Spam-Status: No, score=-5.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,FORGED_SPF_HELO,KAM_DMARC_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE,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 Adhemerval,=0A= =0A= > Right, I was not trying to be clever here and acquire might be a more=0A= > strict memory order.=0A= >=0A= > And I haven't replied yet to you atomic refactor, but I also think changi= ng=0A= > step by step is indeed better than changing all the atomic altogether.=0A= =0A= Well that's what I did, I split into about 15-20 patches rather than a sing= le one.=0A= =0A= > Do you think using relaxed on all atomic is suffice here?=0A= =0A= Indeed, adding acquire on these counters will not ensure correct memory ord= ering.=0A= =0A= Note this particular code looks very unsafe - it is not clear to me how it = blocks=0A= other threads from accessing new elements before they are properly initiali= zed.=0A= Also the counters that are being updated atomically are read without atomic= =0A= accesses, so may get a cached value or something newer - you don't know.=0A= =0A= Cheers,=0A= Wilco=