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

Oleg Nesterov
2019-05-15T14:38:58Z

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().

> + if (!tsk)
> + ret = -ESRCH;
> + else if (unlikely(!thread_group_leader(tsk)))
> + ret = -EINVAL;

it seems that you can do a single check

tsk = pid_task(p, PIDTYPE_TGID);
if (!tsk)
ret = -ESRCH;

this even looks more correct if we race with exec changing the leader.

Oleg.