rcu: Add grace-period information to RCU CPU stall warnings

This commit causes the last grace period started and completed to be
printed on RCU CPU stall warning messages in order to aid diagnosis.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutree.c

@@ -947,8 +947,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
 	raw_spin_unlock_irqrestore(&rnp->lock, flags);
 
 	print_cpu_stall_info_end();
-	printk(KERN_CONT "(detected by %d, t=%ld jiffies)\n",
-	       smp_processor_id(), (long)(jiffies - rsp->gp_start));
+	pr_cont("(detected by %d, t=%ld jiffies, g=%lu, c=%lu)\n",
+	       smp_processor_id(), (long)(jiffies - rsp->gp_start),
+	       rsp->gpnum, rsp->completed);
 	if (ndetected == 0)
 		printk(KERN_ERR "INFO: Stall ended before state dump start\n");
 	else if (!trigger_all_cpu_backtrace())
@@ -975,7 +976,8 @@ static void print_cpu_stall(struct rcu_state *rsp)
 	print_cpu_stall_info_begin();
 	print_cpu_stall_info(rsp, smp_processor_id());
 	print_cpu_stall_info_end();
-	printk(KERN_CONT " (t=%lu jiffies)\n", jiffies - rsp->gp_start);
+	pr_cont(" (t=%lu jiffies g=%lu c=%lu)\n",
+		jiffies - rsp->gp_start, rsp->gpnum, rsp->completed);
 	if (!trigger_all_cpu_backtrace())
 		dump_stack();