linux-kernel - [PATCH v9 7/8] rcu/tree: Setschedule gp ktread to SCHED

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Message-Id: <20190719140000.31694-8-juri.lelli@redhat.com>
Date:   Fri, 19 Jul 2019 15:59:59 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     peterz@...radead.org, mingo@...hat.com, rostedt@...dmis.org,
        tj@...nel.org
Cc:     linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org, lizefan@...wei.com,
        longman@...hat.com, dietmar.eggemann@....com,
        cgroups@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>
Subject: [PATCH v9 7/8] rcu/tree: Setschedule gp ktread to SCHED_FIFO outside of atomic region

sched_setscheduler() needs to acquire cpuset_rwsem, but it is currently
called from an invalid (atomic) context by rcu_spawn_gp_kthread().

Fix that by simply moving sched_setscheduler_nocheck() call outside of
the atomic region, as it doesn't actually require to be guarded by
rcu_node lock.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
---
 kernel/rcu/tree.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 980ca3ca643f..32ea75acba14 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3123,13 +3123,13 @@ static int __init rcu_spawn_gp_kthread(void)
 	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)
+		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) {
+	if (kthread_prio)
 		sp.sched_priority = kthread_prio;
-		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
-	}
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	wake_up_process(t);
 	rcu_spawn_nocb_kthreads();
-- 
2.17.2