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Tue, 12 Nov 2019 17:40:55 +0000 From: "Harris, Robert" To: "tglx@linutronix.de" , "mingo@redhat.com" , "peterz@infradead.org" , "dvhart@infradead.org" CC: "linux-kernel@vger.kernel.org" , "Harris, Robert" Subject: Help requested: futex(..., FUTEX_WAIT_PRIVATE, ...) returns EPERM Thread-Topic: Help requested: futex(..., FUTEX_WAIT_PRIVATE, ...) returns EPERM Thread-Index: AQHVmYBWNvZci+jLJUqod1Huijtj9w== Date: Tue, 12 Nov 2019 17:40:55 +0000 Message-ID: Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=robert.harris@alertlogic.com; x-originating-ip: [165.225.81.101] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 5863aed9-66c7-4753-a0b0-08d7679778a9 x-ms-traffictypediagnostic: BYAPR20MB2245: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:10000; x-forefront-prvs: 021975AE46 x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(136003)(376002)(39850400004)(396003)(366004)(346002)(199004)(189003)(478600001)(102836004)(6506007)(36756003)(5660300002)(99286004)(54906003)(55236004)(6486002)(8676002)(66066001)(33656002)(6116002)(3846002)(25786009)(476003)(2616005)(486006)(2906002)(186003)(8936002)(26005)(6436002)(2201001)(76116006)(66946007)(110136005)(4326008)(66476007)(64756008)(81166006)(81156014)(66446008)(91956017)(316002)(66556008)(71200400001)(86362001)(14454004)(107886003)(305945005)(5024004)(71190400001)(14444005)(256004)(7736002)(2501003)(6512007);DIR:OUT;SFP:1102;SCL:1;SRVR:BYAPR20MB2245;H:BYAPR20MB2726.namprd20.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX:1; received-spf: None (protection.outlook.com: alertlogic.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: GkzuYyFoe2/iwDh3WnFchPivlxqcaTmXywQOItFKFeoZb+Ui7Xb3uX7GUpezPq6gzith4AZ1PRNeOK3zbSN7DNPolFOOfBZPRlXMnW7B2Gv5lFOwfGYzGhmfVbkILxrIa55wOGlFMq6JKU5h8fQM+fIXxHNy82vlDiSLz7UNeLzWRHSGdMBtZX4VgGvF4SJIymj0iL9CIKR/qhPGnGOhJBzcaQUpv2RHApwryCmworToEWLD/X3sNqL3xMO3kZYNEcpvo+cEPvSXuvtTVIYntV0siuYqIOakG1lxd04NsZ3yIsXuWj1GWUUzApRVD9DreKD4dPZ6DHAZDtpuMh8skZqCmliFiVM1BtmPDAXNNdb/MysvlmDcVpjzgNmyZWE93LQqwAKv+LUoBEcmVpuiaUIc6uHq034Buq7+FJRBu7+7Dp7HZoGi2cwJBkSnM3lO Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: alertlogic.com X-MS-Exchange-CrossTenant-Network-Message-Id: 5863aed9-66c7-4753-a0b0-08d7679778a9 X-MS-Exchange-CrossTenant-originalarrivaltime: 12 Nov 2019 17:40:55.6470 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 04151827-cb2a-4231-9c24-1ef5ffc408eb X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: Cicr87e9LYyAK6F0gsBgSIP85mYmXwfl7AaHcpt3GtfBPD+JNMCzIRy76bqvs0Vk+ilJqEH5Xt+UWdBVeoP5mzO69l33nV/CJESZmEFvGwU= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR20MB2245 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I am investigating an issue on 4.9.184 in which futex() returns EPERM intermittently for futex(uaddr, FUTEX_WAIT_PRIVATE, val, &timeout, NULL, 0) The failure affects an application in an AWS lambda; traditional debugging approaches vary from difficult to impossible. I cannot reproduce the problem at will, instrument the kernel, install a new kernel or get an application core dump. Understanding the circumstances under which EPERM can be returned for FUTEX_WAIT_PRIVATE would be useful but it is not a documented failure mode. I have spent some time looking through futex.c but have not found anything yet. I would be grateful for a hint from someone more knowledgeable. Please address/cc me on any reply. Thanks, Robert Harris Confidentiality Notice | This email and any included attachments may be pri= vileged, confidential and/or otherwise protected from disclosure. Access to= this email by anyone other than the intended recipient is unauthorized. If= you believe you have received this email in error, please contact the send= er immediately and delete all copies. If you are not the intended recipient= , you are notified that disclosing, copying, distributing or taking any act= ion in reliance on the contents of this information is strictly prohibited.