Re: [PATCH v1 1/1] waitid: Add support for waiting for the current process group

[Oleg Nesterov]

On 08/14, Christian Brauner wrote:
>
> On Wed, Aug 14, 2019 at 02:29:10PM +0200, Oleg Nesterov wrote:
> > On 08/14, christian.brau...@ubuntu.com wrote:
> > >
> > >   case P_PGID:
> > >           type = PIDTYPE_PGID;
> > > -         if (upid <= 0)
> > > +         if (upid < 0)
> > >                   return -EINVAL;
> > > +
> > > +         if (upid == 0)
> > > +                 pid = get_pid(task_pgrp(current));
> >
> > this needs rcu lock or tasklist_lock, this can race with another thread
> > doing sys_setpgid/setsid (see change_pid(PIDTYPE_PGID)).
>
> Oh, I naively assumed task_pgrp() would take an rcu lock...

but it would not help ;)

> though I think we should be fine with just rcu_read_lock().

Yes,

Oleg.