linux-kernel - [PATCH 2/5] rcu/tree: Fix SCHED

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Message-Id: <20190801111541.742613597@infradead.org>
Date:   Thu, 01 Aug 2019 13:13:50 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        Juri Lelli <juri.lelli@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH 2/5] rcu/tree: Fix SCHED_FIFO params

A rather embarrasing mistake had us call sched_setscheduler() before
initializing the parameters passed to it.

Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: "Paul E. McKenney" <paulmck@...ux.ibm.com>
Fixes: 1a763fd7c633 ("rcu/tree: Call setschedule() gp ktread to SCHED_FIFO outside of atomic region")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/rcu/tree.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3234,13 +3234,13 @@ static int __init rcu_spawn_gp_kthread(v
 	t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
 	if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
 		return 0;
-	if (kthread_prio)
+	if (kthread_prio) {
+		sp.sched_priority = kthread_prio;
 		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+	}
 	rnp = rcu_get_root();
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	rcu_state.gp_kthread = t;
-	if (kthread_prio)
-		sp.sched_priority = kthread_prio;
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	wake_up_process(t);
 	rcu_spawn_nocb_kthreads();