[PATCH 1/2] pid: add pidfd_open()

[Oleg Nesterov]

On 05/15, Oleg Nesterov wrote:
>
> On 05/15, Christian Brauner wrote:
> >
> > +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.