linux-kernel - [PATCH v4 1/2] rcu: Eliminate rcu_state.nocb_is

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Date:   Wed, 17 Aug 2022 09:42:52 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        "Josh Triplett" <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, <rcu@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH v4 1/2] rcu: Eliminate rcu_state.nocb_is_setup

'rcu_state.nocb_is_setup' is initialized to true only if 'rcu_nocb_mask'
successfully allocates memory. So it can be replaced by
'cpumask_available(rcu_nocb_mask)'. More importantly, the latter is more
intuitive, and it has been used in several places.

Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 kernel/rcu/tree.h      | 1 -
 kernel/rcu/tree_nocb.h | 8 +++-----
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index d4a97e40ea9c3e2..06f659c63d2d192 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -375,7 +375,6 @@ struct rcu_state {
 	arch_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
 						/* Synchronize offline with */
 						/*  GP pre-initialization. */
-	int nocb_is_setup;			/* nocb is setup from boot */
 };
 
 /* Values for rcu_state structure's gp_flags field. */
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 0a5f0ef41484518..ff763e7dc53551f 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -69,7 +69,6 @@ static int __init rcu_nocb_setup(char *str)
 			cpumask_setall(rcu_nocb_mask);
 		}
 	}
-	rcu_state.nocb_is_setup = true;
 	return 1;
 }
 __setup("rcu_nocbs", rcu_nocb_setup);
@@ -1215,7 +1214,7 @@ void __init rcu_init_nohz(void)
 	struct rcu_data *rdp;
 
 #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
-	if (!rcu_state.nocb_is_setup) {
+	if (!cpumask_available(rcu_nocb_mask)) {
 		need_rcu_nocb_mask = true;
 		offload_all = true;
 	}
@@ -1235,10 +1234,9 @@ void __init rcu_init_nohz(void)
 				return;
 			}
 		}
-		rcu_state.nocb_is_setup = true;
 	}
 
-	if (!rcu_state.nocb_is_setup)
+	if (!cpumask_available(rcu_nocb_mask))
 		return;
 
 #if defined(CONFIG_NO_HZ_FULL)
@@ -1299,7 +1297,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
 	struct task_struct *t;
 	struct sched_param sp;
 
-	if (!rcu_scheduler_fully_active || !rcu_state.nocb_is_setup)
+	if (!rcu_scheduler_fully_active || !cpumask_available(rcu_nocb_mask))
 		return;
 
 	/* If there already is an rcuo kthread, then nothing to do. */
-- 
2.25.1