Re: [PATCH v4] signal: add taskfd_send_signal() syscall

[Jürg Billeter]

On Thu, 2018-12-06 at 14:12 +0100, Florian Weimer wrote:
> * JÃrg Billeter:
> 
> > On Thu, 2018-12-06 at 13:30 +0100, Florian Weimer wrote:
> > > * Christian Brauner:
> > > 
> > > > /* zombies */
> > > > Zombies can be signaled just as any other process. No special error will be
> > > > reported since a zombie state is an unreliable state (cf. [3]).
> > > 
> > > I still disagree with this analysis.  If I know that the target process
> > > is still alive, and it is not, this is a persistent error condition
> > > which can be reliably reported.  Given that someone might send SIGKILL
> > > to the process behind my back, detecting this error condition could be
> > > useful.
> > 
> > As I understand it, kill() behaves the same way. I think it's good that
> > this new syscall keeps the behavior as close as possible to kill().
> 
> No, kill does not behave in this way because the PID can be reused.
> The error condition is not stable there.

The PID can't be reused as long as it's a zombie. It can only be reused
when it has been wait()ed for. Or am I misunderstanding something?

JÃrg