That doesn't mean that naive single-threaded code is necessarily interrupt-safe. If the allocator is interrupted and the interrupt service routine needs to make use of the allocator's data structures for any reason there could very much be a conflict.

This particular algorithm is focused on GPUs, so I'm not clear on the applicability. However I did want to clear up the idea that there are no concurrency concerns for single-threaded library code, an assumption that's been the source of many bugs.