diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index feb3ac1dc5d5..f87c9d6d36fc 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -162,7 +162,7 @@ static inline bool rcu_seq_done_exact(unsigned long *sp, unsigned long s)
 {
 	unsigned long cur_s = READ_ONCE(*sp);
 
-	return ULONG_CMP_GE(cur_s, s) || ULONG_CMP_LT(cur_s, s - (2 * RCU_SEQ_STATE_MASK + 1));
+	return ULONG_CMP_GE(cur_s, s) || ULONG_CMP_LT(cur_s, s - (3 * RCU_SEQ_STATE_MASK + 1));
 }
 
 /*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e4c0ce600b2b..131fb463ba68 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1801,10 +1801,14 @@ static noinline_for_stack bool rcu_gp_init(void)
 
 	/* Advance to a new grace period and initialize state. */
 	record_gp_stall_check_time();
+	/*
+	 * A new wait segment must be started before gp_seq advanced, so
+	 * that previous gp waiters won't observe the new gp_seq.
+	 */
+	start_new_poll = rcu_sr_normal_gp_init();
 	/* Record GP times before starting GP, hence rcu_seq_start(). */
 	rcu_seq_start(&rcu_state.gp_seq);
 	ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
-	start_new_poll = rcu_sr_normal_gp_init();
 	trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
 	rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);
 	raw_spin_unlock_irq_rcu_node(rnp);
@@ -3357,14 +3361,17 @@ EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
  */
 void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
 {
-	struct rcu_node *rnp = rcu_get_root();
-
 	/*
 	 * Any prior manipulation of RCU-protected data must happen
 	 * before the loads from ->gp_seq and ->expedited_sequence.
 	 */
 	smp_mb();  /* ^^^ */
-	rgosp->rgos_norm = rcu_seq_snap(&rnp->gp_seq);
+
+	// Yes, rcu_state.gp_seq, not rnp_root->gp_seq, the latter's use
+	// in poll_state_synchronize_rcu_full() notwithstanding.  Use of
+	// the latter here would result in too-short grace periods due to
+	// interactions with newly onlined CPUs.
+	rgosp->rgos_norm = rcu_seq_snap(&rcu_state.gp_seq);
 	rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence);
 }
 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full);