sched/debug: Show task state in /proc/sched_debug

Currently we print the runnable task in /proc/sched_debug, but
there is no task state information.

We don't know which task is in the runqueue and which task is sleeping.

Add task state in the runnable task list, like this:

  runnable tasks:
   S           task   PID         tree-key  switches  prio     wait-time             sum-exec        sum-sleep
  -----------------------------------------------------------------------------------------------------------
   S   watchdog/239  1452       -11.917445      2811     0         0.000000         8.949306         0.000000 7 0 /
   S  migration/239  1453     20686.367740         8     0         0.000000     16215.720897         0.000000 7 0 /
   S  ksoftirqd/239  1454    115383.841071        12   120         0.000000         0.200683         0.000000 7 0 /
  >R           test 21287      4872.190970       407   120         0.000000      4874.911790         0.000000 7 0 /autogroup-150
   R           test 21288      4868.385454       401   120         0.000000      3672.341489         0.000000 7 0 /autogroup-150
   R           test 21289      4868.326776       384   120         0.000000      3424.934159         0.000000 7 0 /autogroup-150

Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <cj.chengjian@huawei.com>
Cc: <huawei.libin@huawei.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1502095463-160172-2-git-send-email-xiexiuqi@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/debug.c

@@ -421,13 +421,19 @@ static char *task_group_path(struct task_group *tg)
 }
 #endif
 
+static const char stat_nam[] = TASK_STATE_TO_CHAR_STR;
+
 static void
 print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
 {
-	if (rq->curr == p)
-		SEQ_printf(m, "R");
-	else
-		SEQ_printf(m, " ");
+	unsigned long state;
+
+	if (rq->curr == p) {
+		SEQ_printf(m, ">R");
+	} else {
+		state = p->state ? __ffs(p->state) + 1 : 0;
+		SEQ_printf(m, " %c", state < sizeof(stat_nam) - 1 ? stat_nam[state] : '?');
+	}
 
 	SEQ_printf(m, "%15s %5d %9Ld.%06ld %9Ld %5d ",
 		p->comm, task_pid_nr(p),
@@ -456,9 +462,9 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
 
 	SEQ_printf(m,
 	"\nrunnable tasks:\n"
-	"            task   PID         tree-key  switches  prio"
+	" S           task   PID         tree-key  switches  prio"
 	"     wait-time             sum-exec        sum-sleep\n"
-	"------------------------------------------------------"
+	"-------------------------------------------------------"
 	"----------------------------------------------------\n");
 
 	rcu_read_lock();