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Date: Tue, 8 Jan 2019 12:17:42 -0600
From: "Serge E. Hallyn" <serge@hallyn.com>
To: Tycho Andersen <tycho@tycho.ws>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
        Christian Brauner <christian@brauner.io>,
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Subject: Re: [PATCH v7 2/2] selftests: add tests for pidfd_send_signal()
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On Tue, Jan 08, 2019 at 10:58:43AM -0700, Tycho Andersen wrote:
> On Tue, Jan 08, 2019 at 11:54:15AM -0600, Serge E. Hallyn wrote:
> > On Tue, Jan 08, 2019 at 10:53:06AM -0700, Tycho Andersen wrote:
> > > On Wed, Jan 02, 2019 at 05:16:54PM +0100, Christian Brauner wrote:
> > > > +			/*
> > > > +			 * Stop the child so we can inspect whether we have
> > > > +			 * recycled pid PID_RECYCLE.
> > > > +			 */
> > > > +			close(pipe_fds[0]);
> > > > +			ret = kill(recycled_pid, SIGSTOP);
> > > > +			close(pipe_fds[1]);
> > > > +			if (ret) {
> > > > +				(void)wait_for_pid(recycled_pid);
> > > > +				_exit(PIDFD_ERROR);
> > > > +			}
> > > 
> > > Sorry for being late to the party, but I wonder if this whole thing
> > > couldn't be simplified with /proc/sys/kenrel/ns_last_pid?
> > 
> > no, bc it's not namespaced :)
> 
> Huh? It looks like it is...
> 
> static int pid_ns_ctl_handler(struct ctl_table *table, int write,
>                 void __user *buffer, size_t *lenp, loff_t *ppos)
> {
>         struct pid_namespace *pid_ns = task_active_pid_ns(current);
>         struct ctl_table tmp = *table;
>         int ret, next;
> 
>         if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
>                 return -EPERM;
> 
>         ...

Oh - hah, but that's ns_last_pid.  You'd want pid_max.  And that one
is not namespaced.