[PATCH AUTOSEL 5.2 027/185] rcu/tree: Call setschedule() gp ktread to SCHED_FIFO outside of atomic region

[Sasha Levin]

From: Juri Lelli <juri.lelli@xxxxxxxxxx>

[ Upstream commit 1a763fd7c6335e3122c1cc09576ef6c99ada4267 ]

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@xxxxxxxxxxxxx>
Tested-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: bristot@xxxxxxxxxx
Cc: claudio@xxxxxxxxxxxxxxx
Cc: lizefan@xxxxxxxxxx
Cc: longman@xxxxxxxxxx
Cc: luca.abeni@xxxxxxxxxxxxxxx
Cc: mathieu.poirier@xxxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: tj@xxxxxxxxxx
Cc: tommaso.cucinotta@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20190719140000.31694-8-juri.lelli@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 980ca3ca643fb..32ea75acba144 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();
-- 
2.20.1