What is a fastbin chunk?

General
1

Getting this weird one and I’m not even sure what I should be looking for. This is in a preemptive thread on Linux. A lock imbalance often presents itself “incorrect guard value” so I’m guessing that this is something to do with two threads trying to alter the same data?

malloc_consolidate(): unaligned fastbin chunk detected
2

Sounds like the memory allocator is doing some consolidation of unused memory and it has resulted in or found a structure that isn’t aligned on a memory boundary of some sort. That could be due to one thread freeing some memory while another is perhaps writing to it, or a neighboring element.