linux-kernel - [PATCH rcu 06/10] rcu: Make priority of grace-period thread consistent

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Date:   Fri,  4 Feb 2022 15:24:02 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, Alison Chaiken <achaiken@...ora.tech>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 06/10] rcu: Make priority of grace-period thread consistent

From: Alison Chaiken <achaiken@...ora.tech>

The priority of RCU grace period threads is set to kthread_prio when
they are launched from rcu_spawn_gp_kthread().  The same is not true
of rcu_spawn_one_nocb_kthread().  Accordingly, add priority elevation
to rcu_spawn_one_nocb_kthread().

Signed-off-by: Alison Chaiken <achaiken@...ora.tech>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree_nocb.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 1e40519d1a05a..ea889cbfc3b95 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1239,6 +1239,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
 	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
 	struct rcu_data *rdp_gp;
 	struct task_struct *t;
+	struct sched_param sp;
 
 	if (!rcu_scheduler_fully_active || !rcu_nocb_is_setup)
 		return;
@@ -1248,6 +1249,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
 		return;
 
 	/* If we didn't spawn the GP kthread first, reorganize! */
+	sp.sched_priority = kthread_prio;
 	rdp_gp = rdp->nocb_gp_rdp;
 	mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
 	if (!rdp_gp->nocb_gp_kthread) {
@@ -1258,6 +1260,8 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
 			return;
 		}
 		WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
+		if (kthread_prio)
+			sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
 	}
 	mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
 
-- 
2.31.1.189.g2e36527f23