pid: change task_state() to use task_ppid_nr_ns()

to simplify the code.

Note that only tpid and max_fds really need rcu_read_lock(), we could move
task_ppid_nr_ns/task_tgid_nr_ns/task_numa_group_id/get_task_cred outside of
rcu read section.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/20250810173620.GA20007@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: oleg-nesterov

fs/proc/array.c

@@ -157,13 +157,11 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 	unsigned int max_fds = 0;
 
 	rcu_read_lock();
-	ppid = pid_alive(p) ?
-		task_tgid_nr_ns(rcu_dereference(p->real_parent), ns) : 0;
-
 	tracer = ptrace_parent(p);
 	if (tracer)
 		tpid = task_pid_nr_ns(tracer, ns);
 
+	ppid = task_ppid_nr_ns(p, ns);
 	tgid = task_tgid_nr_ns(p, ns);
 	ngid = task_numa_group_id(p);
 	cred = get_task_cred(p);