[PATCH] do_task_stat() use pid_alive()

Use pid_alive() rather than testing for a zero value of ->pid.  Is the right
thing to do and addresses an oops dereferencing real_parent which one person
reported.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/proc/array.c

@@ -370,7 +370,7 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
 			stime += task->signal->stime;
 		}
 	}
-	ppid = task->pid ? task->group_leader->real_parent->tgid : 0;
+	ppid = pid_alive(task) ? task->group_leader->real_parent->tgid : 0;
 	read_unlock(&tasklist_lock);
 
 	if (!whole || num_threads<2)