linux-kernel - [tip:sched/core] rcu/tree: Call setschedule() gp ktread to SCHED

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Message-ID: <tip-1a763fd7c6335e3122c1cc09576ef6c99ada4267@git.kernel.org>
Date:   Thu, 25 Jul 2019 09:24:10 -0700
From:   tip-bot for Juri Lelli <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     juri.lelli@...hat.com, hpa@...or.com, mingo@...nel.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        dietmar.eggemann@....com
Subject: [tip:sched/core] rcu/tree: Call setschedule() gp ktread to
 SCHED_FIFO outside of atomic region

Commit-ID:  1a763fd7c6335e3122c1cc09576ef6c99ada4267
Gitweb:     https://git.kernel.org/tip/1a763fd7c6335e3122c1cc09576ef6c99ada4267
Author:     Juri Lelli <juri.lelli@...hat.com>
AuthorDate: Fri, 19 Jul 2019 15:59:59 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
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@...radead.org>
Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: bristot@...hat.com
Cc: claudio@...dence.eu.com
Cc: lizefan@...wei.com
Cc: longman@...hat.com
Cc: luca.abeni@...tannapisa.it
Cc: mathieu.poirier@...aro.org
Cc: rostedt@...dmis.org
Cc: tj@...nel.org
Cc: tommaso.cucinotta@...tannapisa.it
Link: https://lkml.kernel.org/r/20190719140000.31694-8-juri.lelli@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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);
 	wake_up_process(t);
 	rcu_spawn_nocb_kthreads();