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

[Florian Weimer]

* JÃrg 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?

Hmm, that's a fair point.  So the original interface is just broken.

Florian