Our malloc() implementation is actually async signal safe, by way of deferring signal delivery. I suspect the issue in this case is rather that malloc() isn't fork() safe in an multi-threaded program. If one thread calls fork() while another is currently in malloc() (or free(),...) the child process will inherit a locked mutex.
The solution is to register respective atfork() hooks for the memory allocator. They would acquire the mutex pre-fork() and release it post-fork(), thus ensuring that the child finds the memory allocator in a usable state.
