rcu: Test synchronous RCU grace periods at the end of rcu_init()

This commit tests synchronize_rcu() and synchronize_rcu_expedited()
at the end of rcu_init(), in addition to the test already at the
beginning of that function.  These tests are run only in kernels built
with CONFIG_PROVE_RCU=y.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree.c

@@ -4849,6 +4849,8 @@ void __init rcu_init(void)
 	// Kick-start any polled grace periods that started early.
 	if (!(per_cpu_ptr(&rcu_data, cpu)->mynode->exp_seq_poll_rq & 0x1))
 		(void)start_poll_synchronize_rcu_expedited();
+
+	rcu_test_sync_prims();
 }
 
 #include "tree_stall.h"

kernel/rcu/update.c

@@ -220,6 +220,7 @@ void rcu_test_sync_prims(void)
 {
 	if (!IS_ENABLED(CONFIG_PROVE_RCU))
 		return;
+	pr_info("Running RCU synchronous self tests\n");
 	synchronize_rcu();
 	synchronize_rcu_expedited();
 }