I first did this work in zfsonlinux and SmartOS.  This should bring zfsonlinux, SmartOS, and illumos in sync.
https://github.com/zfsonlinux/zfs/commit/d45d7f08fa56f94fc9577a6578cb411071a42e8d
SmartOS, as a private option:
https://github.com/joyent/illumos-joyent/commit/b322ba367cdb75882f1cede5a8b22c7fd17ced94
SmartOS, now public:
https://github.com/joyent/illumos-joyent/commit/d0efab8443fcce33c336a009d253617419db9909

This has been exercised in SmartOS for a couple weeks, with it in the critical path for various bhyve instance operations (create, storage management) without any issues.  Testing of the upstreamin work recorded in illumos#11355.