From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from YT5PR01CU002.outbound.protection.outlook.com (mail-canadacentralazon11021128.outbound.protection.outlook.com [40.107.192.128]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5110A2DC764 for ; Thu, 12 Mar 2026 21:28:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.192.128 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773350890; cv=fail; b=U9ViI653Au7vUsQoZwqiHZUF/oXA5PkxDM5n4lHNviB1/jHJZd3ukHAJcXLHf5ka2xgeNWXEsLmIyzUSJMOa6wHfUetwuXMyF76DvyvhPbzwo9JTSvRu3NKHILPD+7mHCQcOKYeC6xfXlR6mQJDEPLQV9ejiJubR/trAWYDxAFU= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773350890; c=relaxed/simple; bh=LcUwRjkM1HvC2YVkEDP0X/VrG2v7b5PFKKG8me9YVRY=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=syx531yv3qKgpWGzDc187sHu6aq6KoUUjMwMeUFUUfY6uzbOqEDqfhf2Y4kA7I1lkgAiQvQPbh74x6sZNBuq7yYTmBIaYexyiBtrLw8JokvvX4lU1wNEF2lHZJqdhvgfNYtzWlBPy2L8RnJhdfyXoi4q+Cmi6crAvuZan9sNdr8= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com; spf=pass smtp.mailfrom=efficios.com; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b=ey0a7cjH; arc=fail smtp.client-ip=40.107.192.128 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=efficios.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="ey0a7cjH" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=MPP/3riRmeiIzn8UamjNk2O5rZ2yLUFDKwwe177o3mndytbvXnSW9Pin4OaKijxvKIost4pp49F/B2uOQnxuBXdiy5+UvYrVjXIbbF74L0XuAzbXzs7Z3YJSxaH4amV4YlQ1UOHCUG9Y8GqIQJa9XMtJNTvOPyjWokSQ9F8eRARz93emXNOnxXaQArobtYVnTOLWzE5I9mH2gSr/nHfuFeZpWyZsAvx4baha/+fxi7Hgp2gaDpJJ7KYoZGzTZHFzuDqvNdl3RxlwwMyfnAcnXi69kk3o2Oab+Zn/txXIdsZEJFf1R4EuMit+6fw7DRmleSo6pHl5Fk+uYXEg2yZ9Gg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=o4LvCCr5zBKS2/kbBKPvtQTLeoAI2d4+RHPvmlKc9aY=; b=tVI+2OgE8uWlXbTAlZJoIHHNXFb7MCH04nYD4Ur4Yy7FzFSfKaYQCk894uPUzqfDk+rj0Bez0psjWhsPxsZ/xqpMB6yvIPWD7L+VCrHJeLFdB6xmCO7rwr/IUiOYt3Gdz3BJafo85v7UNz2b4AVU1nEtfg08e14kr/yirqa33ZnWuasBWtYj6mgD4n9E/LRH+odD+q0pAVu6IhvdcVgRFWO9Ir7VLuFsi0nTWmipSrASa1NQeplQANEOvZ7PZXDCREeUxmeUYxxDuFN73Ks7INZcf7pHkArf19afMTfVrtzdmA5lifQ8yrW23++NQzlJz7zwuTV2p/X6NAYxWtpXIA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=efficios.com; dmarc=pass action=none header.from=efficios.com; dkim=pass header.d=efficios.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=o4LvCCr5zBKS2/kbBKPvtQTLeoAI2d4+RHPvmlKc9aY=; b=ey0a7cjHw2YhMOYbTdIDEe/0nDUYKAHuREQxTYwiXlSRscj26npgVFbEyxUowOyvpk1EOD7iYVLbAZ82k6ZRdgWbn+ffCTBLx16okbFDLyHVKghYrAGecBxAsugHKAHMgY86WLkFrLbErBgjKq4xgZr7i7TW06GcuJh3SxswQGuZ4n1sYx3pedSED2kE9vlaLc/9QiK4lG88ZTAR5f+ZSY/MeaLWIEuDiSMp3RKoXUfISvFEOdlWxB8GLFn98WClOr0jCTUnKXuuNm7fJ4K/b2jSVC5M2Welv4GHgbQ3PsNiqoYqUsxzTUEC4cekN+ztZLWy7PWQZuIed2WxGvmv8g== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=efficios.com; Received: from YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:be::5) by YT4PR01MB10407.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:e9::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9700.15; Thu, 12 Mar 2026 21:28:02 +0000 Received: from YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM ([fe80::6004:a862:d45d:90c1]) by YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM ([fe80::6004:a862:d45d:90c1%3]) with mapi id 15.20.9700.015; Thu, 12 Mar 2026 21:28:01 +0000 Message-ID: <70d8b2d0-4079-4688-97d8-67038214a710@efficios.com> Date: Thu, 12 Mar 2026 17:28:02 -0400 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] futex: Introduce __vdso_robust_futex_unlock To: Thomas Gleixner , =?UTF-8?Q?Andr=C3=A9_Almeida?= Cc: linux-kernel@vger.kernel.org, Carlos O'Donell , Sebastian Andrzej Siewior , Peter Zijlstra , Florian Weimer , Rich Felker , Torvald Riegel , Darren Hart , Ingo Molnar , Davidlohr Bueso , Arnd Bergmann , "Liam R . Howlett" References: <20260311185409.1988269-1-mathieu.desnoyers@efficios.com> <2993f778-c4f4-4aa8-8e42-1dca4d5e29e1@igalia.com> <87ikb0pzpv.ffs@tglx> From: Mathieu Desnoyers Content-Language: en-US In-Reply-To: <87ikb0pzpv.ffs@tglx> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: YQBPR01CA0156.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:7e::20) To YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:be::5) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: YT2PR01MB9175:EE_|YT4PR01MB10407:EE_ X-MS-Office365-Filtering-Correlation-Id: 40b75c9e-044d-41a2-e6fb-08de807e3d07 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|10070799003|1800799024|376014|7416014|22082099003|56012099003|18002099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM;PTR:;CAT:NONE;SFS:(13230040)(366016)(10070799003)(1800799024)(376014)(7416014)(22082099003)(56012099003)(18002099003);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 2 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?T3R4aXNKM1dEeDRDamdQZXpubGxaNmxKN1lCd2FtcU9NRk9nSjhRWUlVWk9J?= =?utf-8?B?YngwbS83V2RWSW9QZEVRbC8rYlhnM2ZGWk9vU1JjdkhxeUJZZ0tEWmVLQnNO?= =?utf-8?B?aHc1QklXM3R4YWk1RkpFazNxNEV0M1Fna1ZHODdLZ1JDYjFQQUkrRXB0QnNN?= =?utf-8?B?aHpLN0p2S2NWR1JtR2hqczNZM3BNRjRrakVmOWZscXJEWUxaTVR3SHRQeTJv?= =?utf-8?B?cHdrRnY5ZngwUDBuVXlGSG9zdVFnYlFiV2RIdWh2bDdBY1ZyeUo1Y2F6NzZz?= =?utf-8?B?QXR4c2JqOExXVzF3YnBuc25TeTM1RUZVYzJ4Q09xLzJVdzdCdkZnUVQ1Q1JT?= =?utf-8?B?ekc4Z2Y1c0tzenYxTXRxdmlwNUFUZ0ZuWGZLYzBoYzFEZ3h1UTFuUm12bGtt?= =?utf-8?B?L3hKMmtXbGNyQnJjOXpwTjQ2WDhtdElMZE5yWHlmbVdRZERXd0hWT2Znb0ZX?= =?utf-8?B?MTdHNGdEY0J0NDVBVkNTZmZ4cm5XQjcwb2taZ290UDRLVk5jaU5kYXFaMkVN?= =?utf-8?B?bTN2bU43SERjdUZjVS9zcnlGeVM3aEY5a25oajlLRHJpNERpVWRaM1hjaWxX?= =?utf-8?B?L2g3MU96Y0s4NVZoREhUdWhJSmtHNnVSRTZUL2JYWC9RaFJ5RGdITXoxcXJC?= =?utf-8?B?UDVnZHZiTFNKb0JHaXRTQUt4Nmo3YktnbmZzQk9ReFJER0Jia041bi9KRExF?= =?utf-8?B?Z1IxWUZOb0Zya0x6TlJQSytDcjgwYUxzb2VFT2lQazV2eUpid1lMdll3dWVi?= =?utf-8?B?OGhJMFdXblVmajQycHZ6dzFxVGhvdnRyaEprdG1xcmxHeTREeXM4VjhzZVh3?= =?utf-8?B?Q2wrdVlIS25LS2xrN21TU2tOME0xZFcrTjdNL0UySHJURFdBZWFtNUJobU1E?= =?utf-8?B?bmdvSUlvSzNwdWw2ZHV6L01kSW9mOWhpQjNZeVd1OFlZUTI2NDhzVFNGVUo3?= =?utf-8?B?a1NVa2tkaFFsYjFrWHpKdlhpUVp2Wk5Rbmd0cVJMcG5hWjBkSU9DZlVlMVdZ?= =?utf-8?B?VFNLZnI2cDc3WGdodUJzQTJQQ0RBdjN6clVKUk5YQzhKdXRyNjFudUNXREdX?= =?utf-8?B?K0ZVSmgwdW8zNzZ0ejUvZXIrazZkRUpaeTBGZHR5VGdSOUIxa3l1b1l3cVg1?= =?utf-8?B?bzI5eTlHOHdML0dKZWVCWHB0Q1dkRWtHc2U5RW9TVVhMbk1CZllUcFZSV2dT?= =?utf-8?B?ZTlSemVzVkdmVHNxTnNWWkROR2xnYjFzUUVhNFRZcjYxU3FNaTB1aWJldzFI?= =?utf-8?B?ejdMQXNFRXlyZjYvajJkRDJ4MUxMM0Z6dmxQWWw2SnhoR1c0R283NVhvVjhw?= =?utf-8?B?TDZqQVZ4MUtUd0dDQVRCR0NOY3V4bDVTYnNkeUpWWUd1N1RvMk1iNldzeUJo?= =?utf-8?B?TTZqTFM5SXNlV0c4eXh1MXU0QVpxUTNpVWg5dmt1U0lDekhVRUF2b3EyN0pR?= =?utf-8?B?bjhBK3dldXNURE9rdlBlNHRTdTdTdHFBcDB1c0l4SmxuazIzU2NTTHZrWU83?= =?utf-8?B?YUFkSkwvV0t1d3VkSTU1clYxdkd4anBJck1OS0ZsWDg1ZFBMNUFFejEvbm9r?= =?utf-8?B?d2J2Tk1aQkhDVmpFSzNlOXNRRDRXMzRtVmh2RmZPS3lpUUtUZkJSMTI1UmxJ?= =?utf-8?B?TGpjdytqN1dtQldNR3VGcGRaTHNOTnRhYzg0aUdMUzU2aXNRNnA0SHBzU1N3?= =?utf-8?B?TElhQjFiNGlUalNrU2xPaWRGeW80eTl6d1BYMWtuWEFSeXFHWWY5bGJFeFpW?= =?utf-8?B?aDI1eW1FTml0NW80dVBGWWZPUEgyY3pyOEJsb0Y1VXZpRmFpZU5EVHc4WDAy?= =?utf-8?B?ZWJWVnZrVnpHN3p2dkthN1JqSVhZYTM5dVViZEdkcmdqdjFyNGNjOW1NYWF4?= =?utf-8?B?cUpxa1dOUnZudnA1UHF1bVpSWlpDY1g4bW1Fd1AyakpIRmJrckk4VXRiUWxM?= =?utf-8?B?YWk2S2hETURlS1JOMDZKU01GMy9JdU14MlIvMlBHM1JNSVFaSW5ySkJlcVJN?= =?utf-8?B?ZDBlZ0d4Zm9sTGRJbGdkYmF5Qi9FTThhK1Q5N1QwcFo5R01DaUhjcHRyZnhB?= =?utf-8?B?aTRWS0FQMFVIZFFaMXdsWDAyT2N2WndZd3o0N2Myb2lhTzNTTjQ1UFljbUp0?= =?utf-8?B?Tm9MUEhTUWhjU3J2aE5Nb3dWZzhEbmpDVmJRZWJnUkx3L1orQmhWY0cvaFZt?= =?utf-8?B?YXZOclcvYTA4MktIZlhFQkRwQ1lNb1VRZDhJMk5XalJSR0RlLzRLeTd3dTlX?= =?utf-8?B?QkcrMEx5Z2JaNVdWTTRCeXNSMlRTUWlPU21KR2xqbFlSK25tRm1jY0xTK09L?= =?utf-8?B?dmtWTnFUc0liSmQ4N3BUZ0lIdUREQ1RzbXA2UllsL2x6VFFaRm9pQnNibzBY?= =?utf-8?Q?0/o0ad7XdQk4GS+QR3xOCsLfrn6Q+jxtLkhmMzcsQcnns?= X-MS-Exchange-AntiSpam-MessageData-1: jak2RZGHcjR8mhqZl4+qhWWBVLUlXv9HIcU= X-OriginatorOrg: efficios.com X-MS-Exchange-CrossTenant-Network-Message-Id: 40b75c9e-044d-41a2-e6fb-08de807e3d07 X-MS-Exchange-CrossTenant-AuthSource: YT2PR01MB9175.CANPRD01.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Mar 2026 21:28:01.2811 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4f278736-4ab6-415c-957e-1f55336bd31e X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 9llgfrvY/mL2WO7+7NtHG1yoUuL1A6FmvHb7mMR7HqGZl0WhNLu9Og3wv08RNP3t4PjAsZkg54wuZ7taR3j3Q7dBHKCV9M6LGT8CFiOjspM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: YT4PR01MB10407 On 2026-03-12 16:19, Thomas Gleixner wrote: > On Thu, Mar 12 2026 at 10:46, André Almeida wrote: >> Em 11/03/2026 15:54, Mathieu Desnoyers escreveu: >> I would also have `uval` instead of `val = 0`, because even though the >> most common semanthics for futex is that (LOCK_FREE == 0), futex has no >> predetermined semanthics of what each value means, and the userspace is >> free to choose what value they want to choose for a free lock. > > That's true for non-robust futexes, but robust futexes have clearly > defined semantics vs. the userspace value: > > 0: unlocked > != 0: PID of the owner > > So uval is useless as the unlock value can't be anything else than 0, > no? Yes, that was my original assumption, hence why I did not have a "val" parameter (and internally used 0 within the vDSO). I can go back to that behavior in a following version. Just to confirm: for robust PI futexes, the value used for the cmpxchg store would always be 0 as well, right ? If that's the case, having an input "val" is useless there too, and we just need a pointer to an expected/loaded value. I'm also not convinced that adding a _u32 suffix to the vDSO symbol is useful if the robust futexes already define the futex value to be 32-bit wide. Thanks, Mathieu > > Thanks, > > tglx -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com