Re: [PATCH 1/1] mm: introduce process_reap system call

[Jan Engelhardt]

On Thursday 2021-07-08 08:05, Suren Baghdasaryan wrote:
>>
>> That explains very clearly the requirement, but it raises the question
>> why this isn't an si_code flag for rt_sigqueueinfo, reusing the existing
>> system call.
>
>I think you are suggesting to use sigqueue() to deliver the signal and
>perform the reaping when a special value accompanies it. This would be
>somewhat similar to my early suggestion to use a flag in
>pidfd_send_signal() (see:
>https://lore.kernel.org/patchwork/patch/1060407) to implement memory
>reaping which has another advantage of operation on PIDFDs instead of
>PIDs which can be recycled.
>kill()/pidfd_send_signal()/sigqueue() are supposed to deliver the
>signal and return without blocking. Changing that behavior was
>considered unacceptable in these discussions.

The way I understood the request is that a userspace program (or perhaps two,
if so desired) should issue _two_ calls, one to deliver the signal,
one to perform the reap portion:

	uinfo.si_code = SI_QUEUE;
	sigqueue(pid, SIGKILL, &uinfo);
	uinfo.si_code = SI_REAP;
	sigqueue(pid, SIGKILL, &uinfo);