rcu: Add mutex for rcu boost kthread spawning and affinity setting

As we handle parallel CPU bringup, we will need to take care to avoid
spawning multiple boost threads, or race conditions when setting their
affinity. Spotted by Paul McKenney.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a4c25a6283b0..d1d1a8c51223 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4570,6 +4570,7 @@ static void __init rcu_init_one(void)
 			init_waitqueue_head(&rnp->exp_wq[2]);
 			init_waitqueue_head(&rnp->exp_wq[3]);
 			spin_lock_init(&rnp->exp_lock);
+			mutex_init(&rnp->boost_kthread_mutex);
 		}
 	}