On 05/15, Oleg Nesterov wrote:

On 05/15, Christian Brauner wrote:

quoted

+SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
+{
+	int fd, ret;
+	struct pid *p;
+	struct task_struct *tsk;
+
+	if (flags)
+		return -EINVAL;
+
+	if (pid <= 0)
+		return -EINVAL;
+
+	p = find_get_pid(pid);
+	if (!p)
+		return -ESRCH;
+
+	rcu_read_lock();
+	tsk = pid_task(p, PIDTYPE_PID);

You do not need find_get_pid() before rcu_lock and put_pid() at the end.
You can just do find_vpid() under rcu_read_lock().

Ah, sorry. Somehow I forgot you need to call pidfd_create(pid), you can't
do this under rcu_read_lock().

So I was wrong, you can't avoid get/put_pid.

Oleg.