A WT_PUBLISH wraps the btree->checkpoint_gen store, this historically was paired with a WT_ORDERED_READ that has since been removed.

The publish is here

The ordered read was here. The change that introduced the publish and read is here.

This field is read without barriers in at least 2 places in the code, but it isn't clear what this variable is ordered with so its possible no barrier is required on the writer side. This will require a more in-depth review.