linux-kernel - [PATCH 2/4] RCU: make priority of grace-period thread consistent

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Date:   Tue, 11 Jan 2022 15:32:51 -0800
From:   Alison Chaiken <achaiken@...ora.tech>
To:     tglx@...utronix.de
Cc:     peterz@...radead.org, paulmck@...nel.org,
        valentin.schneider@....com, frederic@...nel.org,
        linux-kernel@...r.kernel.org, glenn@...ora.tech,
        alison@...-devel.com, Alison Chaiken <achaiken@...ora.tech>
Subject: [PATCH 2/4] RCU: make priority of grace-period thread consistent

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>
---
 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 8fdf44f8523f..08b5c0042979 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1183,7 +1183,9 @@ static void rcu_spawn_one_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;
 
+	sp.sched_priority = kthread_prio;
 	/*
 	 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
 	 * then nothing to do.
@@ -1199,6 +1201,8 @@ static void rcu_spawn_one_nocb_kthread(int cpu)
 		if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))
 			return;
 		WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
+		if (kthread_prio)
+			sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
 	}
 
 	/* Spawn the kthread for this CPU. */
-- 
2.32.0