This is not a production bug so threat it accordingly.

The race:
Initially, _fpInfo was ( 1 << 31 ).
1. Thread 1 enters FailPoint::slowShouldFailOpenBlock() and increments the _fpInfo to ( 1 << 31 + 1)
2. Thread 2 enters disableFailPoint() and reads _fpInfo into currentVal
3. Thread 1 enters FailPoint::shouldFailCloseBlock() and decrements _fpInfo to ( 1 << 31 )
4. Thread 2 spins forever

Even though this is not production failure, someone may copy-paste this pattern into production code. Atomics are subtle and must be treated with care.

Fix: load _fpInfo each time inside loop. Same for enableFailPoint().