[PATCH 04/16] rcu/nocb: Only (re-)initialize segcblist when needed on CPU up

[Frederic Weisbecker]

Simply checking if the segcblist is enabled is enough to know if we
need to initialize it or not. It's safe to check within hotplug
machine.

Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
---
 kernel/rcu/tree.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4c5a1ac54fa6..f74a9ba62c12 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4066,14 +4066,13 @@ int rcutree_prepare_cpu(unsigned int cpu)
 	rdp->dynticks_nesting = 1;	/* CPU not up, no tearing. */
 	rcu_dynticks_eqs_online();
 	raw_spin_unlock_rcu_node(rnp);		/* irqs remain disabled. */
+
 	/*
-	 * Lock in case the CB/GP kthreads are still around handling
-	 * old callbacks.
+	 * Only non-NOCB CPUs that didn't have early-boot callbacks need to be
+	 * (re-)initialized.
 	 */
-	rcu_nocb_lock(rdp);
-	if (rcu_segcblist_empty(&rdp->cblist)) /* No early-boot CBs? */
+	if (!rcu_segcblist_is_enabled(&rdp->cblist))
 		rcu_segcblist_init(&rdp->cblist);  /* Re-enable callbacks. */
-	rcu_nocb_unlock(rdp);
 
 	/*
 	 * Add CPU to leaf rcu_node pending-online bitmask.  Any needed
-- 
2.25.1