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McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Boqun Feng , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Davidlohr Bueso , rcu@vger.kernel.org References: <20260626004301.1632168-1-joelagnelf@nvidia.com> Content-Language: en-US From: Joel Fernandes In-Reply-To: <20260626004301.1632168-1-joelagnelf@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BLAPR03CA0143.namprd03.prod.outlook.com (2603:10b6:208:32e::28) 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_|DM4PR12MB6207:EE_ X-MS-Office365-Filtering-Correlation-Id: edb8c922-3582-4619-49c5-08ded31c2680 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|23010399003|376014|7416014|56012099006|11063799006|22082099003|18002099003; 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Once stuck, the pending > gate in rcu_read_unlock_special() silently suppresses all future arming > attempts on that CPU. The series adds PENDING -> IDLE transitions at the > missing sites (patches 1-7), including the case where the deferred-QS > irq-work handler may run between segments of a compound section (per Paul > McKenney's counter-example) and the softirq deferred-QS arming path. > > Patch 8 adds a per-CPU rescue hrtimer that bounds the worst-case > deferred-QS reporting latency: when the irq-work handler lands in a clean > (non-reader, non-compound) context it reports the quiescent state directly > via the new rcu_preempt_deferred_qs_try_report() helper, and the rescue timer > reuses the same helper so that, under preempt=none, the QS report is quick > without depending on the scheduler. The rescue timer is cancelled from the > normal deferred-QS report path so it does not fire once the quiescent state > has already been reported. > > This version is rebased on top of Paul's latest rcu/dev branch. The > rcutorture reader-end deboost test patches that were folded into v3 are now > in rcu/dev and have been dropped here. The git tree below additionally > carries two debug-only commits on top of the series ([TEST COMMIT], not for > merge): a detector that WARNs if defer_qs_pending is stuck at GP cleanup, > and an rcutorture tweak that gives the async deboost mechanisms up to 500us > before warning. Applied alone on unmodified mainline, the detector reliably > fires within 5 minutes under TREE03 rcutorture; with the full fix applied I > could not reproduce the issue. > > The git tree with all patches can be found at: > git://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux.git (tag: rcu-dqs-stuck-v4-20260625) Just fyi, the 2 "[TEST COMMIT]" patches not for merge are in the above tag. I missed including it in the LKML posting, but they are not for merge anyway.