[PATCH RFC tip/core/rcu 5/7] rcu: Avoid clobbering early boot callbacks

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

When a CPU comes online, it initializes its callback list.  This
is a bad thing if this is the first time that the CPU has come
online and if that CPU has early boot callbacks.  This commit therefore
avoid initializing the callback list if there are callbacks present,
in which case the initial call_rcu() did the initialization for us.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ff2e42ebb64b..02fa29a4d104 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3584,7 +3584,8 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
 	rdp->qlen_last_fqs_check = 0;
 	rdp->n_force_qs_snap = rsp->n_force_qs;
 	rdp->blimit = blimit;
-	init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
+	if (!rdp->nxtlist)
+		init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
 	rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 	rcu_sysidle_init_percpu_data(rdp->dynticks);
 	atomic_set(&rdp->dynticks->dynticks,
-- 
1.8.1.5