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McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Boqun Feng , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , rcu@vger.kernel.org, Joel Fernandes Subject: [PATCH v2 5/7] rcu: clear defer_qs_pending at expedited IPI entry Date: Tue, 26 May 2026 18:50:12 -0400 Message-Id: <20260526225014.314734-6-joelagnelf@nvidia.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260526225014.314734-1-joelagnelf@nvidia.com> References: <20260526225014.314734-1-joelagnelf@nvidia.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: BL1PR13CA0105.namprd13.prod.outlook.com (2603:10b6:208:2b9::20) To DS0PR12MB6486.namprd12.prod.outlook.com (2603:10b6:8:c5::21) 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: DS0PR12MB6486:EE_|CH3PR12MB8353:EE_ X-MS-Office365-Filtering-Correlation-Id: adf7cfc3-8edb-406c-27bb-08debb792e67 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|366016|1800799024|11063799006|18002099003|22082099003|56012099006; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?pWsk4oGmFgMRr56fZVRwIF94ocGNE7+m5Tbwjv3ASQC0HpdU+4MWxhybH1vD?= =?us-ascii?Q?kei1FX1cJqzNmoDw81uozdKdxx0KiyhlRD9cfhBr6XCXN3q8mVDIIW1H0aEM?= =?us-ascii?Q?WDZ/MvxGaHzohQe0zEXFV6h+WA0pfItgn+j9KLkCreM4R603mhtCVqAzcJzK?= =?us-ascii?Q?0vCfx455y3MHOWQRLthTixcTvc4Lc+qRslEq0gmXKSq82lGcmOorVGDUzszQ?= =?us-ascii?Q?h/bUNJcR+rGXesMrkZN0hrDSTNyj1Fa9mrMoXXXosWkYCQ4eSQDP5tDFKEx8?= =?us-ascii?Q?9Ff2Dso9Qw+rnKY6irGdc//y77ovKuI4RFmTV88k44ImYDUWKUW5OAQ0/owl?= =?us-ascii?Q?BvGuQ6HjAX3XgungMVlihxpD2UGNBiCQYibO7wDs/9umVffDJslL6oYEkONn?= =?us-ascii?Q?NaHtDgTFFTj164N3FmsDWIgxVmfOaYxoxrlfrEIbIbyzVeW6DPqr1y4P1G8w?= =?us-ascii?Q?sNVjR4P/HRRSLInvZkCrg4I3bYHu0ZtYyLz6UavFHSJQe1NfXQq0oJnzs6bs?= =?us-ascii?Q?Pzdn/IGWuetbDE0DYVAqMUHo1pnubnlub5O2GQcJSKl4YI7msH+/3QyLwp14?= =?us-ascii?Q?Ko2c1B4Je8OHC5q0B9pHTsGT9dug3UemMBzJWcNUJDTwjTofKClrBGxOFTVY?= =?us-ascii?Q?meYKJt1Efmej1ctpDrunDOyGghtTOTPKPtLVa0bFo0pmo1LtYxh+AWDOcnEE?= =?us-ascii?Q?AJ70QrkFUo3eZVTjTwKerYdRSAolGNlfosRpJj7MaafoOWY5Tno0Ivw26FYl?= =?us-ascii?Q?3QZCEBoi9SjuETeFaalYwwFW4WSWaz8Q8mjCKJSulXn82XUtYYHgL23dRiBL?= =?us-ascii?Q?L/0c9xTowHAODwxHDLHAJBIjRgDk+rXtvLB4+GVPCW47QIMb0d7uTF/j3z4T?= =?us-ascii?Q?GgSPsxhOhxaxfM2fd5lPlkdKtjjhL+S/kgH0Rgku1xM6L84fwpeDFI9XH1vE?= =?us-ascii?Q?kcOu3R+4iqVtuMLjmfEeuvv9kH8t3QcDr9p2SkN46MNJY+V5sy03KCkwTPUd?= =?us-ascii?Q?6CulyzNb7E2o8gObX4US2dmn2VMXKPBlpU6AV71mLMRr8tXGomVB8sLQnSFM?= =?us-ascii?Q?OHacomf0W5CUZpplQqAkbxja+EXJaS+lkBGmWtyJzt3bJDylNoN4B2rN22jE?= =?us-ascii?Q?vzEhihso2AzB5d24CEhIftSsPepAAzWrsXohSNo/JnDUNlqQuwmFtc1UdqIo?= =?us-ascii?Q?SfR+yGHme2PZg9MVmjEFHJWHTOqWC1B3qR/sabtLrWwmji7g3AklRgAxnKgh?= =?us-ascii?Q?Yxn6pzaemWe2hxGc38IqvMsdrfjnG/vTBso4yx4Ma7ZrOJ5L4V8pUVy3ySrB?= =?us-ascii?Q?qYajVQimKGcRHrIlo1zjKWHa4X/L65Zipqyl09yQC4xza5qc1iLUxVLwA0W/?= =?us-ascii?Q?C4C0qOdAry7RVMclmwQCe3UjLtpOvkFTBhqyVbsgSG58nbTkLnN6pjQkiwiy?= =?us-ascii?Q?Cxe35Bsj1nEyfwYzysCrBwkRrcR4Mt/FtBA4TJ+5fIvQSwQBR13ZuSh9E3Wn?= =?us-ascii?Q?pk7WDTQ/+NsEHA4B/cj5RaSx1y6jzfTTeD/nDIxEuPAFRIFl8hPpblpPtxu/?= =?us-ascii?Q?/9bDUybiYaLnVhNmnMY+0fTY5rVNqBpXcD1/7MFWdRquTe3A3cJgFyBR9TJW?= =?us-ascii?Q?+5BJSBaeqOgdNKj/ehD02+TeKA0qwk7yfuyz7KvwXTZm/OcHXiaXWUAZPURo?= =?us-ascii?Q?fe4eq6WzsiUdKkMJsK/iQwKqpH//6bmcX4LF0X+v0YPDrhN2gNEmc0BBEme6?= =?us-ascii?Q?uzazGcLf4w=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: adf7cfc3-8edb-406c-27bb-08debb792e67 X-MS-Exchange-CrossTenant-AuthSource: DS0PR12MB6486.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 May 2026 22:50:27.8547 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: mJqHjVjYukjH0DXLjCaJmWCudmIE4jo7I1XQoG5LxItk+XIQLXCAe7ZqRAIs8zFXqxNFm2Yg5+/tTBGiGMN64w== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB8353 The per-CPU clear in __note_gp_changes() (from an earlier commit) runs only when the local CPU notices a normal-GP advance. When an expedited GP arrives at a CPU whose defer_qs_pending is already PENDING, rcu_read_unlock_special() may skip irq_work queuing due to the pending gate. Clear defer_qs_pending on the IPI target right in rcu_exp_handler(). This makes it possible for any arming attempt that follows the IPI within the current GP to be able to queue irq_work again, allowing completion expedited GPs quickly than waiting for one scheduler tick. Signed-off-by: Joel Fernandes --- kernel/rcu/tree_exp.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 82cada459e5d..f8564a041879 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -763,6 +763,12 @@ static void rcu_exp_handler(void *unused) READ_ONCE(rdp->cpu_no_qs.b.exp))) return; + /* + * Clear defer_qs_pending so arming attempts following this IPI + * within the current GP can queue irq_work again. + */ + rcu_defer_qs_clear(rdp); + /* * Second, the common case of not being in an RCU read-side * critical section. If also enabled or idle, immediately -- 2.34.1