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Wed, 25 Feb 2026 05:11:14 -0600 Received: from [10.24.73.74] (uda0492258.dhcp.ti.com [10.24.73.74]) by lelvem-mr06.itg.ti.com (8.18.1/8.18.1) with ESMTP id 61PBB8c14039653; Wed, 25 Feb 2026 05:11:09 -0600 Message-ID: <166cf8ef-9991-499d-902a-58bd1e227388@ti.com> Date: Wed, 25 Feb 2026 16:42:39 +0530 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird CC: , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH net 1/3] net: ethernet: ti: am65-cpsw-nuss: set irq_disabled after disabling RX IRQ To: Jakub Kicinski References: <20260220041431.372610-1-s-vadapalli@ti.com> <20260220041431.372610-2-s-vadapalli@ti.com> <20260223184803.739c17a7@kernel.org> <20260224155432.15ded392@kernel.org> Content-Language: en-US From: Siddharth Vadapalli In-Reply-To: <20260224155432.15ded392@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-C2ProcessedOrg: 333ef613-75bf-4e12-a4b1-8e3623f5dcea X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL6PEPF0001AB56:EE_|DM3PPFBD8703CAB:EE_ X-MS-Office365-Filtering-Correlation-Id: 82774578-3419-473a-1a22-08de745e97b7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|34070700014|36860700013|1800799024|82310400026|7416014|376014; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:198.47.21.194;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:flwvzet200.ext.ti.com;PTR:ErrorRetry;CAT:NONE;SFS:(13230040)(34070700014)(36860700013)(1800799024)(82310400026)(7416014)(376014);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: V07cf7qAV8/VsNW5aaNCP8i7eoJetY4mEtb1KWgbFyt1Gsc3K6313fVT7BQB9YXHDpKAEbWRmDLmSrklXNigt5G112mj+71QPtZbIGiZLv3xzXo6X1jNl78D/ugPHKXG+wz6xiPfvWmoZlwoja8bBOpm485Bi0iN07ExLrTTmYmz1mKzbBEx3l88CQLU9T6/VOs/A3rc37pLfCldNjqQmShXcog7/86wU495sujz/eQyvmbQ36STFpM/YcjOvNVaiJ2y/ZV6lU79MTFJ58PLu/ZAiKRj5FU8ozxKFdw9s1d877LNIdVF3dOvfnnP+IFoaXBkK8rSmfkzBWy5Clp15i9CWiMiMTIatWX1fn7HFcBMGLGnGRDN40li3jdW2z91PvRFeuI37Td6MHk2UKwFDzamo3XtXZctlkiYtOjHu2yxiO2l0mDxONDswKSKhhe3 X-OriginatorOrg: ti.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Feb 2026 11:11:15.3063 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 82774578-3419-473a-1a22-08de745e97b7 X-MS-Exchange-CrossTenant-Id: e5b49634-450b-4709-8abb-1e2b19b982b7 X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=e5b49634-450b-4709-8abb-1e2b19b982b7;Ip=[198.47.21.194];Helo=[flwvzet200.ext.ti.com] X-MS-Exchange-CrossTenant-AuthSource: BL6PEPF0001AB56.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM3PPFBD8703CAB On 25/02/26 05:24, Jakub Kicinski wrote: > On Tue, 24 Feb 2026 10:40:05 +0530 Siddharth Vadapalli wrote: >> CPU1 sees irq_disabled being 'true' and before it updates it to 'false', if >> CPU2 also sees irq_disabled >> being 'true', both CPU1 and CPU2 will enter the IF-condition and eventually >> invoke enable_irq(). > > I think the races are just between NAPI and the HARD IRQ context. > There can only be one NAPI scheduled for a queue, I assume. Yes. An already executing RX NAPI Handler (scheduled via net_rx_action) sees 'irq_disabled' set by the HARD IRQ handler. The RX NAPI Handler then executes 'enable_irq()' for the RX IRQ before it is actually disabled by the HARD IRQ handler using disable_irq_nosync(). > >> Please let me know if this is what you were referring to. I will use atomic >> APIs at all places to update >> 'irq_disabled'. > > I recommend a spin lock, unless you can measure as significant > difference. Locks and atomics have similar cost on many CPUs. > And juggling local state, IRQ state, and NAPI state atomically > will get tricky. Updates to 'irq_disabled' are performed by: 1. Hard IRQ Handler sets irq_disabled to true. => Since there can be only one IRQ for a given RX Queue, we can be certain that there is no race w.r.t. setting it to true. 2. NAPI RX Handler sets irq_disabled to false if currently true. => This is the part I am unsure of but if a single instance of the NAPI RX Handler will be scheduled in an SMP environment as well, there won't be a race between multiple processors as the following will cannot happen simultaneously on multiple CPUs running the RX Handler: irq_disabled = false; enable_irq(); Regards, Siddharth.