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client-ip=165.204.84.17; helo=satlexmb08.amd.com; pr=C Received: from satlexmb08.amd.com (165.204.84.17) by CH1PEPF0000AD76.mail.protection.outlook.com (10.167.244.53) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9542.4 via Frontend Transport; Fri, 16 Jan 2026 04:39:08 +0000 Received: from SATLEXMB04.amd.com (10.181.40.145) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.17; Thu, 15 Jan 2026 22:39:07 -0600 Received: from satlexmb08.amd.com (10.181.42.217) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Thu, 15 Jan 2026 22:39:07 -0600 Received: from [10.136.34.241] (10.180.168.240) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Thu, 15 Jan 2026 22:39:03 -0600 Message-ID: <6eabf604-9168-47fb-8fd8-b2f0d985db6a@amd.com> Date: Fri, 16 Jan 2026 10:08:57 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] cpufreq: Pass the policy to cpufreq_driver->adjust_perf() To: Viresh Kumar CC: Huang Rui , "Gautham R. Shenoy" , Mario Limonciello , "Rafael J. Wysocki" , Srinivas Pandruvada , Len Brown , Sebastian Andrzej Siewior , Clark Williams , Bert Karwatzki , , , , Perry Yuan References: <20260114085113.21378-1-kprateek.nayak@amd.com> <20260114085113.21378-3-kprateek.nayak@amd.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Received-SPF: None (SATLEXMB04.amd.com: kprateek.nayak@amd.com does not designate permitted sender hosts) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH1PEPF0000AD76:EE_|DM6PR12MB4401:EE_ X-MS-Office365-Filtering-Correlation-Id: 5b34ec55-98ee-42d0-c92a-08de54b92fe1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|36860700013|376014|1800799024|82310400026|13003099007|7053199007; X-Microsoft-Antispam-Message-Info: =?utf-8?B?VG53ZnpWRGJieWE0V0JDS0RQN0NWb3ZUMVB0cUtqNXJLTjlKL0s4Tlg0eUNK?= =?utf-8?B?Yyt6QWcydDRYbWtXSkk4YnN3elc0NmMwNEQvVmtLNnBVK3ZTVW9IOHhDaXpR?= =?utf-8?B?Vkc4KzdrZDhMR0h2Nk01azRIalBYWTZaenhkb25Ndi9rSXZDRmN5R1dwcDJM?= =?utf-8?B?M0l3YmFmSEJjMnZDaXQrZmVqM0xMK1V5eENoVnZlRjU2NXhlbGwxZDlNK21j?= =?utf-8?B?RFFrS3creEJUVnFmUG0vaHRSWlA2R0gzTjZBOVYyakZVSnp5dWVDdU5GMmIr?= =?utf-8?B?U0NaVWlDaE1hc0dMWVlNV3UxbjBIOXFncE9EZTUwT1kydFlCVEU4bndReEtM?= =?utf-8?B?Yy8rQWZpeXlUZ1lLUHVYaTRTVmR1RUNIZGE3dlpjR2lxUGNIaHNROFY0cGMy?= =?utf-8?B?KzlkY1VEWnRsTDhRNkphR1A1Tk5waXI2aXVIcGx2dTVQRE1ocUpTY3lsMU4v?= =?utf-8?B?WkhkNTRpQjBmOVhmQitjK1NtNTQ5a3BkOTdITTdtTGoxR3NXTm0vN0o3MUZh?= =?utf-8?B?amczWkZNRjcvRzA1ZUM3K3FCVjBoeTMwU0pHRnV6b1pzaWN6U0JyTGkzTXBy?= =?utf-8?B?V242ZllRMkNVNTRnMW1NSnN0QTN3MkZITC9KWU8wNkZvMyt1dDlCYVlUWXhJ?= =?utf-8?B?VHJhK0owaDVla0RDTm9oK2FUWXlYcE5HbW55blBxNDMzejJVQllXU0UwMDFu?= =?utf-8?B?TVZ0MGxVQU93YStmVFIwZDEzTEtmalhCSE5rN0dydzRiTTAwbmRZVi9Fdk95?= =?utf-8?B?UUNaRTI2VHBxVTBOWHVFbWFxQnlVWUc3QlBub09IOGF6SUJwdEdMRXpneVpU?= =?utf-8?B?QVAybURhcnlxelMrZHdGeHI0VGxXRkVLM1E2Y3dBVGtXYXo0aE1FcnMyOWFq?= =?utf-8?B?bVBNTEo3NG5uOVQwMkVaWXhveVZJUWd3aExiWElWbVpVNmUvOWVUZjVSWVcy?= =?utf-8?B?SWh2RUxtUnUvb1BuS3ZhWXhCSHRQMVhCRFFCeDRGMGZmbm04RzQrZnVJTHNJ?= =?utf-8?B?Nnp3VCsyMXFEWFNqbGlTUmhhQktJQ0FnUE9JNVNnSjdlc0FXeDhIUzNwYm91?= =?utf-8?B?dVFhLzhhaUxsYW10b25BWVZjNU9nVGNOcVVDVlg2emt0TmI3d1NqOFd0M0pz?= =?utf-8?B?WWMyM2tURk0rRGY3NlBDeWlzbUlmMk5oTlVkTzcraDBRcXFseHQwUmdHUnBt?= =?utf-8?B?MVFLSWRqemVZN3JKNnJHQ0Q2NGNEcCtadmpCdk5nOHlKWldrYzFobG50RXA1?= =?utf-8?B?aDZIMi84QnJ0Z1pJbExQMlpYNWxYUXRTL2NCVEo1Yjc1Q1Z2cjhtY3hBOVJy?= =?utf-8?B?UEtybS9DR210ZWI1Z0JPMXU2V2dSaDZVTlFUbG4vQUljM2dJcFhpOTFodUw5?= =?utf-8?B?aTJWamFVSjRUSk5pb0kwOUg3Rk14SnJaOU9LUDNvQ2NVWVBSZVE0N0wwdDla?= =?utf-8?B?d0lsS2lMbHlLWHB1aTJxU1l2TnQzWnhwcVhyRzJCQi83aTlmZENEWlVNbXhH?= =?utf-8?B?THMzUC9nK09SZHhURDVMOXJ5N2ZhSlFsZTVwaFFiZXppcVYxb0F3K0U1eVJQ?= =?utf-8?B?eDVjWndsc3V0Vi9sbDEyMmx5S3A0eGlxMWJzWDk5UHQrM3I3cmU4dERXdEpz?= =?utf-8?B?dXgwVnU1U0tnU0hZaUwrQ2JjeFlTMG0yYm5DcVJZcjU1VTZicVgvY3hwS1FS?= =?utf-8?B?NjExSXptODB0ODhtaGIvM0RPMEJOY1JET21nNEY2OG1MVksxbUlRYXI5enpJ?= =?utf-8?B?YnV0VFE5SmY4dDBYQzRBL2ZkYUNvdXpsVmt5bGp1VWVPcHV6YldaandpNGti?= =?utf-8?B?OVlpTjVJRndoUjl5bHRyT0s4ZFk1dkFlK2hNNmloMmRzOTBybkdKVEFLa292?= =?utf-8?B?RERwZUliUjJRVFQ5ekhwbzB3eG5MbTRSMXBuVWIvWFFyRWd5ekQrRHNEVW9m?= =?utf-8?B?aERSZDdub3Mzbjd3QjgvOFBySlJOSGFoQmgxUVVONWZEaVVXL3ZoY1g5OTEr?= =?utf-8?B?Vjl1ekYvNklPeG9lVFJISllqMnVDamNtOVl1U2grYllEc1BPK1JpMU9EaFN0?= =?utf-8?B?VFZ0ZHpibEVBYzQ2VFoxVGpZclhCMlBjYXVTWVhDY1lzUEhySjlsVldXYlhm?= =?utf-8?B?YWpvZmdZVHQxOWhtcW1FS2pmUnI4N3cvUDV6dUhFekdITnh6dUp5WFg2VjlR?= =?utf-8?B?NjlJb2lCUGthcnV3RG5VTUliTTlWdFpPWWQ4R0g1bjZlbDQ2cmFRUHVDMTVY?= =?utf-8?B?LzRwSkNhME4wL0RJd3Q0R3ZBamVRPT0=?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb08.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(7416014)(36860700013)(376014)(1800799024)(82310400026)(13003099007)(7053199007);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Jan 2026 04:39:08.1902 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5b34ec55-98ee-42d0-c92a-08de54b92fe1 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CH1PEPF0000AD76.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4401 Hello Viresh, On 1/15/2026 9:44 AM, Viresh Kumar wrote: > On 14-01-26, 08:51, K Prateek Nayak wrote: >> cpufreq_cpu_get() can sleep on PREEMPT_RT in presence of concurrent >> writer(s), however amd-pstate depends on fetching the cpudata via the >> policy's driver data which necessitates grabbing the reference. >> >> Since schedutil governor can call "cpufreq_driver->update_perf()" >> during sched_tick/enqueue/dequeue with rq_lock held and IRQs disabled, >> fetching the policy object using the cpufreq_cpu_get() helper in the >> scheduler fast-path leads to "BUG: scheduling while atomic" on >> PREEMPT_RT [1]. >> >> Pass the cached cpufreq policy object in sg_policy to the update_perf() >> instead of just the CPU. The CPU can be inferred using "policy->cpu". >> >> The lifetime of cpufreq_policy object outlasts that of the governor and >> the cpufreq driver (allocated when the CPU is onlined and only reclaimed >> when the CPU is offlined / the CPU device is removed) which makes it >> safe to be referenced throughout the governor's lifetime. >> >> Reported-by: Bert Karwatzki >> Closes:https://lore.kernel.org/all/20250731092316.3191-1-spasswolf@web.de/ [1] >> Acked-by: Viresh Kumar >> Signed-off-by: K Prateek Nayak > > Ahh, you need to fix the Rust binding as well. Minor change there. Guilty of not having CONFIG_RUST enabled! I've arrived at the following after tasking a look at cpufreq.rs (specifically the fast_switch_callback implementation): (Only build tested currently) diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs index f968fbd22890..bea109f8ff78 100644 --- a/rust/kernel/cpufreq.rs +++ b/rust/kernel/cpufreq.rs @@ -1255,18 +1255,17 @@ impl Registration { /// # Safety /// /// - This function may only be called from the cpufreq C infrastructure. + /// - The pointer arguments must be valid pointers. unsafe extern "C" fn adjust_perf_callback( - cpu: c_uint, + ptr: *mut bindings::cpufreq_policy, min_perf: c_ulong, target_perf: c_ulong, capacity: c_ulong, ) { - // SAFETY: The C API guarantees that `cpu` refers to a valid CPU number. - let cpu_id = unsafe { CpuId::from_u32_unchecked(cpu) }; - - if let Ok(mut policy) = PolicyCpu::from_cpu(cpu_id) { - T::adjust_perf(&mut policy, min_perf, target_perf, capacity); - } + // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the + // lifetime of `policy`. + let policy = unsafe { Policy::from_raw_mut(ptr) }; + T::adjust_perf(policy, min_perf, target_perf, capacity); } /// Driver's `get_intermediate` callback. --- Let me know what you think. If you think this is alright, I'll fold it into this same patch in the next version to preserve bisectiblity with CONFIG_RUST (or should I keep it separate?). Since this is my first time dealing with the rust bindings, comments are highly appreciated. -- Thanks and Regards, Prateek