[tip:sched/core] rcu/tree: Call setschedule() gp ktread to SCHED_FIFO outside of atomic region

From: tip-bot for Juri Lelli
Date: Thu Jul 25 2019 - 14:08:21 EST

Commit-ID: 1a763fd7c6335e3122c1cc09576ef6c99ada4267
Gitweb: https://git.kernel.org/tip/1a763fd7c6335e3122c1cc09576ef6c99ada4267
Author: Juri Lelli <juri.lelli@xxxxxxxxxx>
AuthorDate: Fri, 19 Jul 2019 15:59:59 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 25 Jul 2019 15:55:03 +0200

rcu/tree: Call 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@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>
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 a14e5fbbea46..eb764c24bc4d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3234,13 +3234,13 @@ 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);