Microsoft's 'mimalloc' MIT-licensed allocator is lock-free. Perhaps there's something in there that'd be interesting to read.

  https://github.com/microsoft/mimalloc
  https://github.com/microsoft/mimalloc/blob/master/include/mimalloc-atomic.h

It has gone through testing with Clang's TSAN and (at least some with) the GenMC model checker.

  https://plv.mpi-sws.org/genmc/