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Tue, 13 Feb 2024 05:56:20 +0000 Received: from CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::91b3:fd53:a6ee:8685]) by CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::91b3:fd53:a6ee:8685%4]) with mapi id 15.20.7270.036; Tue, 13 Feb 2024 05:56:20 +0000 From: Ankur Arora To: linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, peterz@infradead.org, torvalds@linux-foundation.org, paulmck@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jpoimboe@kernel.org, mark.rutland@arm.com, jgross@suse.com, andrew.cooper3@citrix.com, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, rostedt@goodmis.org, David.Laight@ACULAB.COM, richard@nod.at, mjguzik@gmail.com, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, Ankur Arora Subject: [PATCH 15/30] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y Date: Mon, 12 Feb 2024 21:55:39 -0800 Message-Id: <20240213055554.1802415-16-ankur.a.arora@oracle.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20240213055554.1802415-1-ankur.a.arora@oracle.com> References: <20240213055554.1802415-1-ankur.a.arora@oracle.com> X-ClientProxiedBy: MW4PR03CA0229.namprd03.prod.outlook.com (2603:10b6:303:b9::24) To CO6PR10MB5409.namprd10.prod.outlook.com (2603:10b6:5:357::14) 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: CO6PR10MB5409:EE_|CY8PR10MB6906:EE_ X-MS-Office365-Filtering-Correlation-Id: 4e167990-1449-4efd-9094-08dc2c588034 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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One reason why this was necessary: lacking preempt-count, the tick handler has no way of knowing whether it is executing in a read-side critical section or not. With PREEMPT_AUTO=y, there can be configurations with (PREEMPT_COUNT=y, PREEMPT_RCU=n). This means that cond_resched() is a stub which does not provide for quiescent states via rcu_all_qs(). So, use the availability of preempt_count() to report quiescent states in rcu_flavor_sched_clock_irq(). Suggested-by: Paul E. McKenney Signed-off-by: Ankur Arora --- kernel/rcu/tree_plugin.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 26c79246873a..9b72e9d2b6fe 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -963,13 +963,16 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) */ static void rcu_flavor_sched_clock_irq(int user) { - if (user || rcu_is_cpu_rrupt_from_idle()) { + if (user || rcu_is_cpu_rrupt_from_idle() || + (IS_ENABLED(CONFIG_PREEMPT_COUNT) && + !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)))) { /* * Get here if this CPU took its interrupt from user - * mode or from the idle loop, and if this is not a - * nested interrupt. In this case, the CPU is in - * a quiescent state, so note it. + * mode, from the idle loop without this being a nested + * interrupt, or while not holding a preempt count. + * In this case, the CPU is in a quiescent state, so note + * it. * * No memory barrier is required here because rcu_qs() * references only CPU-local variables that other CPUs