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

* Jürg Billeter:

On Thu, 2018-12-06 at 14:12 +0100, Florian Weimer wrote:

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* Jürg Billeter:

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On Thu, 2018-12-06 at 13:30 +0100, Florian Weimer wrote:

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* Christian Brauner:

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/* 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