Re: [PATCH v2 2/2] pidfs: ensure consistent ENOENT/ESRCH reporting

Christian Brauner
2025-04-11T15:14:41Z

On Fri, Apr 11, 2025 at 03:54:45PM +0200, Oleg Nesterov wrote:
> For both patches:
>
> Reviewed-by: Oleg Nesterov <oleg@redhat.com>
>
> a minor nit below...
>
> On 04/11, Christian Brauner wrote:
> >
> > int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
> > {
> > - int err = 0;
> > -
> > - if (!(flags & PIDFD_THREAD)) {
> > + scoped_guard(spinlock_irq, &pid->wait_pidfd.lock) {
> > + /*
> > + * If this wasn't a thread-group leader struct pid or
> > + * the task already been reaped report ESRCH to
> > + * userspace.
> > + */
> > + if (!pid_has_task(pid, PIDTYPE_PID))
> > + return -ESRCH;
>
> The "If this wasn't a thread-group leader struct pid" part of the
> comment looks a bit confusing to me, as if pid_has_task(PIDTYPE_PID)
> should return false in this case.

Ok.

>
> OTOH, perhaps it makes sense to explain scoped_guard(wait_pidfd.lock)?
> Something like "see unhash_process -> wake_up_all(), detach_pid(TGID)
> isn't possible if pid_has_task(PID) succeeds".

I'm verbose. I hope you can live with it:

/*
* While holding the pidfd waitqueue lock removing the task
* linkage for the thread-group leader pid (PIDTYPE_TGID) isn't
* possible. Thus, if there's still task linkage for PIDTYPE_PID
* not having thread-group leader linkage for the pid means it
* wasn't a thread-group leader in the first place.
*/

:)