Re: MP-safe IPsec SPD

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

> Date: Mon, 7 Aug 2017 12:40:11 +0900
> From: Ryota Ozaki <ozaki-r%netbsd.org@localhost>
> 
> Thank you for your reviewing! I think I handled all your suggestions.
> Let me know if I missed or misunderstood something.

Thanks!  Looks good.

Couple tiny nits:

- `pserialize critical section' ---> `pserialize read section'?
  (Although we sometimes say `critical section' in conversation, the
  functions are called pserialize_read_enter/exit, and it may not be
  immediately clear whether `pserialize critical section' means a
  nonexclusive reader or an exclusive writer.)

- __read_mostly for key_psz?

While skimming the patch, I noticed an odd global variable acq_seq
that is used only under certain #ifdefs and seems to modified without
any synchronization.  I wonder what it's there for and whether it is
OK for updates to be lost.

> BTW can we have an API to assert that we are in a pserialize critical
> section? Sometimes I want to write something like:
>   KASSERT(pserialize_in_read_critical_section());
> rather than writing the constraint in a comment.

That would be nice to have.  It would require for each machine some
way to ask whether the current IPL is at least some specified IPL,
which as far as I know we don't currently have.  (Nor do we have any
MI way to compare IPLs (both numerical orders are used, so IPL_VM <
IPL_HIGH may be true or false), nor any MI way to query the current
IPL.)