Back in February, the kernel community discussed the removal of a couple of functions
that could be used by loadable modules to gain access to symbols (functions
and data structures) that were not meant to be available to them. That
change was merged
during the 5.7 merge window. This change will break a number of external
modules that depended on the removed functions; since many of those modules
are proprietary, this fact does not cause a great deal of anguish in the
kernel community. But there are a few out-of-tree modules with
GPL-compatible licenses that are also affected by this change; one of those
is LTTng. Fixing LTTng may not be
entirely straightforward.

Source: LWN.net – [$] How to unbreak LTTng