SPL: waiting for kernel to init

[lundman]

Reported by user on forum.

Mojave had a boot-panic situation where we would call wait before the kernel had been fully initialised, and current_process() returned NULL.

I added a delaying action to SPL to wait for current_process() to return !NULL before continuing SPL, with the thoughts that kexts are loaded asynchronously. But if boot stops on this message, it would indicate that we can in fact deadlock the kernel boot process.

Possible solutions:

• Should we change spl_init to start a thread, and immediately return OK in parent, allowing the kernel to keep booting.

• Should we not delay init, but rather fix the places we call wait (all condvars) and replace with sleep() calls untilcurrent_process works.

We might also consider ZFS starting up too early as well, in that SPL might still be waiting to start, but ZFS already tries to use calls in SPL.

[lundman]

openzfsonosx/spl@c3a671b