There's two untrusted code cases here: untrusted DTrace scripts / users, and untrusted targets for inspection. The latter has to be possible to examine, so the observability tools (like DTrace) have to be secure for that purpose. This means you want to make it difficult to overflow buffers in the observability tools.
There's also a need to make sure that even trusted users don't accidentally cause too much observability load. That's why DTrace has a circular probe buffer pool, it's why it drops probes under load, it's why it pre-allocates each probe's buffer by computing how much the probe's actions will write to it, it's why it doesn't allow looping (since that would make the probe's effect less predictable), etc.
Bryan, Adam, and Mike designed it this way two plus decades ago, and Linux still hasn't caught up.
