sched/debug: Print 'tgid' in sched_show_task()

Multiple blocked tasks are printed when the system hangs. They may have
the same parent pid, but belong to different task groups.

Printing tgid lets users better know whether these tasks are from the same
task group or not.
Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230720080516.1515297-1-yajun.deng@linux.dev

kernel/sched/core.c

@@ -9089,9 +9089,9 @@ void sched_show_task(struct task_struct *p)
 	if (pid_alive(p))
 		ppid = task_pid_nr(rcu_dereference(p->real_parent));
 	rcu_read_unlock();
-	pr_cont(" stack:%-5lu pid:%-5d ppid:%-6d flags:0x%08lx\n",
-		free, task_pid_nr(p), ppid,
-		read_task_thread_flags(p));
+	pr_cont(" stack:%-5lu pid:%-5d tgid:%-5d ppid:%-6d flags:0x%08lx\n",
+		free, task_pid_nr(p), task_tgid_nr(p),
+		ppid, read_task_thread_flags(p));
 
 	print_worker_info(KERN_INFO, p);
 	print_stop_info(KERN_INFO, p);