proc_sched_show_task(): use get_nr_threads()

Trivial, use get_nr_threads() helper to read signal->count which we are
going to change.

Like other callers, proc_sched_show_task() doesn't need the exactly
precise nr_threads.

David said:

: Note that get_nr_threads() isn't completely equivalent (it can return 0
: where proc_sched_show_task() will display a 1).  But I don't think this
: should be a problem.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sched_debug.c

@@ -381,15 +381,9 @@ __initcall(init_sched_debug_procfs);
 void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
 {
 	unsigned long nr_switches;
-	unsigned long flags;
-	int num_threads = 1;
-
-	if (lock_task_sighand(p, &flags)) {
-		num_threads = atomic_read(&p->signal->count);
-		unlock_task_sighand(p, &flags);
-	}
 
-	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, p->pid, num_threads);
+	SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, p->pid,
+						get_nr_threads(p));
 	SEQ_printf(m,
 		"---------------------------------------------------------\n");
 #define __P(F) \