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McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang Cc: rcu@vger.kernel.org Subject: [PATCH RFC v1 5/6] rcu: clear defer_qs_pending at expedited IPI entry Date: Fri, 22 May 2026 10:23:39 -0400 Message-Id: <20260522142342.1536533-6-joelagnelf@nvidia.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260522142342.1536533-1-joelagnelf@nvidia.com> References: <20260522142342.1536533-1-joelagnelf@nvidia.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: BL1PR13CA0288.namprd13.prod.outlook.com (2603:10b6:208:2bc::23) 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_|MN0PR12MB5786:EE_ X-MS-Office365-Filtering-Correlation-Id: 018e214c-a5ff-48f7-52e7-08deb80dc9ae X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016|921020|11063799006|22082099003|56012099003|18002099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?BqRRFCHr0NscAv6lmvsBRRLs6J++b7nEfvPIyaiU+bOKvNQLwA5Y9ruz5wEw?= =?us-ascii?Q?D+gfnBJPEwWioR8Odv6kS9v05GAgzKxIc/YOl0zstCigaiRxfGjicsQoYIm4?= =?us-ascii?Q?SvvryxglU0qmBLCqBOhlkj7pmt/0GSpz0Edenr9uBD8lpVkj1zJas7Hp9+Kt?= =?us-ascii?Q?BcH4meG2PAjIA+VdmQFGzDaup/4s4/up3dMO9QNV+39VMoLK29DRnHRf/0hP?= =?us-ascii?Q?2usSK8zB2fymnfJO5cZCSMhbgpcsXRmPIO5hkQMsV7CNAKrhUUT/dkGGeb8O?= =?us-ascii?Q?mxk+5FoR4EQ9DZLtVunj5Fq+clVqii/ha1aPcdMf8wiquIiIQlAZoYHg2SyI?= =?us-ascii?Q?53RIB9q2u9+56jd1SuHqdyMkS56XuzdtkyA9ElcbZREtQOmZ3DXZRhM+4Uof?= =?us-ascii?Q?S2+Wnt9+CIMgW9DkSHRxKGRnD3BGFzssIVhF4BELJuC9fvgUPwPtGDCm0aTK?= =?us-ascii?Q?IdKyW3r3hioNoawGmW1ymw/mZNxBlEAU21koCbXyzc8tZ9vYVT7JY+UlpfSp?= =?us-ascii?Q?GPH1tjiJQGBALY1gwLgpEKDf/sdSqYGlYqpAEdSNQ3czogQBw2/IFykMK+sB?= =?us-ascii?Q?nmmZ1M4SuqOPo3sDIJdFdS5DCTjlBFQ2j54Lg780gahV9foftSjZQTTCQf0w?= =?us-ascii?Q?rCHBoN3iNeKgQkssxqh15b0R28mwq2Dhmm8Qk6aRQPDnSI8lyr+PT2HFsEo1?= =?us-ascii?Q?UiaUrPe6CUmQT8NC/DoOXYoaWIk5e5PR/HKKQ80t1KLVLrOUoe3ckRHSmgyy?= =?us-ascii?Q?+rmQjTRujs0ZNzN7njqwiIknJjaQJQJjBhkG9NBre/RzggHlOKQlIcNPG/+i?= =?us-ascii?Q?+cBxg4OWT9FIAZw7Sfc3ybrqhfku0DhISehk9wG59+fSE/GBEtUZkpvB6ofj?= =?us-ascii?Q?XT5n7TW7S3DVfeb0sf/8t+1OjA0bzbQXqAKrNAPm5948QZytjnzfFEcnQbis?= =?us-ascii?Q?ldFlkg+4RNWt0puX66iRd7c/xALN7T1Jt2smAWbZbDHmv4JM7svBLrUT8dsH?= =?us-ascii?Q?YirVGD05kIPK6+McPByre2vhqMXqgKjrrONs92UKCGyfEKS7qMinwjDLHYNp?= =?us-ascii?Q?JUAGR2t4dyOVEunoYe/mrwMr6fpnQnmyI6UsnDUF/JRVEBOSBUzU11tky64Y?= =?us-ascii?Q?zIRergG2LCuIIb+A60aknybLf3yztRjXEnFr8lDpeSBM19wNYzf/UtEVvRmp?= =?us-ascii?Q?RjNl7bI/byl4RcaLthfbBhgrGsaSZ1P2ARGf+C69KUIZMvqctJ1IGbXUKkcb?= =?us-ascii?Q?YJsaSbiMUWSkcf/qBJQ6eg7dUZ6KwVtQh1cyEuVvZmzgek7O5z/BRswqtzDE?= =?us-ascii?Q?K9zv/EoqcRgZ8W73fK1z4X8zfE/aSlCErkZkC/7lZlYDqs/qGAe9W3e/25rt?= =?us-ascii?Q?+zWP9yr2XPMApIM2iMvUkohT1CHvtQMnDDJtws9zvJ+gqrbDMP60tyQmETlN?= =?us-ascii?Q?P4W1Krgaz9JvNQ+F9vSRJp5AGftnPdXxeqjYjfqrZzmZBNRisvq70zyOrHyi?= =?us-ascii?Q?FKOTdGoBqsjLEdKUcr3GfipHnsqFk6NlawFTBpQQgwfJha00lPm7D3aqp2N8?= =?us-ascii?Q?RJlqM8nMStjg3KPKw38gvYyNpAofoEDdhdIfQn9vXTKs3hc1W3kxBFmw8eXh?= =?us-ascii?Q?YBkepnyaV2cdUlj+LV6wmcrKtQ7BsaQoMqrQOYBUuC3+cUhiCR2cZdI2sCIk?= =?us-ascii?Q?0/0Y4+/IfvyD4YczINw9XAjz8/Ya9qo68jjvI7h2hGwhHiorLRiu0awQDBUT?= =?us-ascii?Q?rDeMfM9TdA=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 018e214c-a5ff-48f7-52e7-08deb80dc9ae X-MS-Exchange-CrossTenant-AuthSource: DS0PR12MB6486.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 May 2026 14:24:09.2560 (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: P87ZNCVN08KvjdYUx2gTZ9Sk3PHyOiirXi9zaVTx66ifps4zfV4PQTGCbpytBA6WQyQVXzJpDh3uVmUmrYb5uQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN0PR12MB5786 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