I think you need to check whether frame == NULL here too; I was able to get a page fault with interrupts disabled here when mucking around with tick probes, and the faulting thread was the idle thread for the cpu.

Elsewhere this is written as #if defined(sun), but it's up to you.

For code under cddl/dev, I usually don't bother keeping the upstream code at all, since we don't merge to that directory from the vendor branch, and the code there tends to be fairly divergent from upstream anyway. But again, up to you.

Is it actually necessary to paranthesize the macro arguments when they're being passed as separate arguments to a function call? It looks like the existing macros do it though, so callout_schedule_sbt_on might as well be consistent.

Yes, thank you, will fix this.

NB: I would prefer cpu_idle() -> cpu_activeclock() path would also set td_intr_frame to something reasonable, but not sure how to do that.

I think that we are gradually switching from 'sun' to 'illumos' in new zfs code, so I applied the same approach here.

Yeah, I noticed that we keep two copies of many dtrace related files in the tree, one that is closer to the upstream and one that is actually used. I think the former is confusing and quite redundant given the vendor area. So, in this instance I decided to keep the original code for the reference.

Good point. I think that the parentheses are not strictly needed here, but I'll fix the code to be consistent.