proc: task_state: ptrace_parent() doesn't need pid_alive() check

p->ptrace != 0 means that release_task(p) was not called, so pid_alive()
buys nothing and we can remove this check.  Other callers already use it
directly without additional checks.

Note: with or without this patch ptrace_parent() can return the pointer to
the freed task, this will be explained/fixed later.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Cc: Sterling Alexander <stalexan@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roland McGrath <roland@hack.frob.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/array.c

@@ -157,19 +157,18 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 	struct user_namespace *user_ns = seq_user_ns(m);
 	struct group_info *group_info;
 	int g;
+	struct task_struct *tracer;
 	const struct cred *cred;
-	pid_t ppid, tpid, tgid, ngid;
+	pid_t ppid, tpid = 0, tgid, ngid;
 	unsigned int max_fds = 0;
 
 	rcu_read_lock();
 	ppid = pid_alive(p) ?
 		task_tgid_nr_ns(rcu_dereference(p->real_parent), ns) : 0;
-	tpid = 0;
-	if (pid_alive(p)) {
-		struct task_struct *tracer = ptrace_parent(p);
-		if (tracer)
-			tpid = task_pid_nr_ns(tracer, ns);
-	}
+
+	tracer = ptrace_parent(p);
+	if (tracer)
+		tpid = task_pid_nr_ns(tracer, ns);
 
 	tgid = task_tgid_nr_ns(p, ns);
 	ngid = task_numa_group_id(p);