Sure, and that alone isn't an unreasonable premise - as he says, intent matters.

But if you're marking interfaces as GPL-only, or implementing taint detection that means if you use a non-SYMBOL_GPL kernel symbol which calls a GPL-only function it treats the non-SYMBOL_GPL symbol as GPL-only and blocks your linking, it gets a bit out of hand.

Building the kernel with certain kernel options makes modules like OpenZFS or OpenAFS not link because of that taint propagation - because things like the lockdep checker turn uninfringing calls into infringing ones.

Or a little while ago, there was a change which broke building on PPC because a change made a non-SYMBOL_GPL call on POWER into a SYMBOL_GPL one indirectly, and when the original author was contacted, he sent a patch reverting the changed symbol, and GregKH refused to pull it into stable, suggesting distros could carry it if they wanted to. (Of course, he had happily merged a change into -stable earlier that just implemented more aggressive GPL tainting and thereby broke things like the aforementioned...)

The Linux kernel has never supported out of tree modules like how ZFS works out of tree.

All ZFS needs to do is just have one of Oracles many lawyers say "CDDL is compatible with GPL". Yet, they Oracle don't.

"All."

It's explicitly not compatible with GPL, though. It has clauses that are more restrictive than GPL, and IIRC some people who contributed to the OpenZFS project did so explicitly without allowing later CDDL license revisions, which removes Oracle's ability to say CDDL-2 or whatever is GPL-compatible.

So even if someone rolled up dumptrucks of cash and convinced Oracle that everything was great, they don't have all the control needed to do that.

To have legal weight, it has to be a signal that you're implementing something that is derivative of kernel code. That's the directly stated intent of EXPORT_SYMBOL_GPL.

But "call an opaque function that saves SIMD state" is obviously not derivative of the kernel code in any way. The more exports that get badly marked this way, the more EXPORT_SYMBOL_GPL becomes indistinguishable from EXPORT_SYMBOL.

I see it as just a kind of "warranty void if seal broken". Don't do this or you may be in violation of the GPL. Maybe a legal court in $country would find in your favour (I'm not convinced it's as clear cut as you imply). Maybe they would find that you willfully infringed, despite the kernel devs clearly warning you not to do it.

The main "legal effect" I see is that you are not willing to take that risk, just like Oracle isn't.

If the goal was to prove someone saw the GPL, then the entire license enforcement mechanism wouldn't be in the kernel.

If enough symbols get restricted without valid copyright-based reasons, modules that legitimately have non-GPL licenses will have to lie to the kernel to get loaded. And that's a stupid situation all around.