rcu: Add diagnostics for rcutorture writer stall warning

This commit adds any in-the-future ->gp_seq_needed fields to the
diagnostics for an rcutorture writer stall warning message.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

@@ -606,11 +606,32 @@ EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
  */
 void show_rcu_gp_kthreads(void)
 {
+	int cpu;
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
 	struct rcu_state *rsp;
 
 	for_each_rcu_flavor(rsp) {
 		pr_info("%s: wait state: %d ->state: %#lx\n",
 			rsp->name, rsp->gp_state, rsp->gp_kthread->state);
+		rcu_for_each_node_breadth_first(rsp, rnp) {
+			if (ULONG_CMP_GE(rsp->gp_seq, rnp->gp_seq_needed))
+				continue;
+			pr_info("\trcu_node %d:%d ->gp_seq %lu ->gp_seq_needed %lu\n",
+				rnp->grplo, rnp->grphi, rnp->gp_seq,
+				rnp->gp_seq_needed);
+			if (!rcu_is_leaf_node(rnp))
+				continue;
+			for_each_leaf_node_possible_cpu(rnp, cpu) {
+				rdp = per_cpu_ptr(rsp->rda, cpu);
+				if (rdp->gpwrap ||
+				    ULONG_CMP_GE(rsp->gp_seq,
+						 rdp->gp_seq_needed))
+					continue;
+				pr_info("\tcpu %d ->gp_seq_needed %lu\n",
+					cpu, rdp->gp_seq_needed);
+			}
+		}
 		/* sched_show_task(rsp->gp_kthread); */
 	}
 }