alinux: kernel: reap zombie process by specified pid

to #26788859

We've met several real-world issues that the child reaper
(i.e. systemd) gets stuck in some aborted status and cann't
reap its zombie children, so we provide the interface to do
By specified the pid.
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: Nzhongjiang-ali <zhongjiang-ali@linux.alibaba.com>

kernel/exit.c

@@ -1765,3 +1765,113 @@ __weak void abort(void)
 	panic("Oops failed to kill thread");
 }
 EXPORT_SYMBOL(abort);
+
+static int force_reap_process(int ptrace, struct task_struct *tsk)
+{
+	struct wait_opts wo;
+	struct pid *pid = get_task_pid(tsk, PIDTYPE_PID);
+	int ret;
+
+	memset(&wo, 0, sizeof(wo));
+	wo.wo_type = PIDTYPE_PID;
+	wo.wo_pid = pid;
+	wo.wo_flags = WEXITED;
+
+	ret = wait_consider_task(&wo, ptrace, tsk);
+	put_pid(pid);
+
+	return ret;
+}
+
+
+static void exit_zombie_process(struct task_struct *tsk)
+{
+	int ret;
+
+	read_lock(&tasklist_lock);
+	ret = force_reap_process(0, tsk);
+	if (ret)
+		goto out;
+	read_unlock(&tasklist_lock);
+out:
+	return;
+}
+
+extern int pid_max;
+#define LEN	8
+static ssize_t reclaim_zombie_process_write(struct file *file,
+					const char __user *ubuf,
+					size_t count, loff_t *ppos)
+{
+	int ret;
+	unsigned int pid;
+	struct task_struct *tsk;
+	char buf[LEN];
+
+	memset(buf, 0, LEN);
+	if (count > LEN - 1) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (copy_from_user(buf, ubuf, count)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	ret = kstrtoint(strstrip(buf), 10, &pid);
+	if (ret)
+		goto out;
+
+	if (pid > pid_max) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* make sure the task status is zombie. */
+	rcu_read_lock();
+	tsk = find_task_by_pid_ns(pid, task_active_pid_ns(current));
+	if (tsk) {
+		get_task_struct(tsk);
+		if (READ_ONCE(tsk->exit_state) != EXIT_ZOMBIE) {
+			rcu_read_unlock();
+			put_task_struct(tsk);
+			ret = -EINVAL;
+			goto out;
+		}
+	} else {
+		rcu_read_unlock();
+		ret = -EINVAL;
+		goto out;
+	}
+	rcu_read_unlock();
+	exit_zombie_process(tsk);
+	put_task_struct(tsk);
+out:
+	return ret == 0 ? count : ret;
+}
+
+const struct file_operations  reclaim_zombie_process_fops = {
+	.owner           = THIS_MODULE,
+	.llseek		 = noop_llseek,
+	.write		 = reclaim_zombie_process_write,
+};
+
+static int __init reclaim_zombie_process_init(void)
+{
+	struct proc_dir_entry *rzp_dir, *rzp_file;
+
+	rzp_dir = proc_mkdir("toolkit", NULL);
+	if (!rzp_dir)
+		return -ENOMEM;
+
+	rzp_file = proc_create("reclaim_zombie_process", 0200, rzp_dir,
+						&reclaim_zombie_process_fops);
+	if (!rzp_file) {
+		remove_proc_entry("toolkit", NULL);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+late_initcall(reclaim_zombie_process_init);