rcu: Remove full memory barrier on boot time eqs sanity check

When the boot CPU initializes the per-CPU data on behalf of all possible
CPUs, a sanity check is performed on each of them to make sure none is
initialized in an extended quiescent state.

This check involves a full memory barrier which is useless at this early
boot stage.

Do a plain access instead.

Signed-off-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Reviewed-by: Neeraj Upadhyay <[email protected]>

Author: Frederic Weisbecker

kernel/rcu/tree.c

@@ -4786,7 +4786,7 @@ rcu_boot_init_percpu_data(int cpu)
 	rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
 	INIT_WORK(&rdp->strict_work, strict_work_handler);
 	WARN_ON_ONCE(ct->dynticks_nesting != 1);
-	WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)));
+	WARN_ON_ONCE(rcu_dynticks_in_eqs(ct_dynticks_cpu(cpu)));
 	rdp->barrier_seq_snap = rcu_state.barrier_sequence;
 	rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
 	rdp->rcu_ofl_gp_state = RCU_GP_CLEANED;