Can someone elaborate on the safety comment in `nix::unistd::fork`

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Hi all, I am trying to understand the safety comment here:
In a multithreaded program, only [async-signal-safe](https://man7.org/linux/man-pages/man7/signal-safety.7.html) functions like `pause` and `_exit` may be called by the child (the parent isn’t restricted). Note that memory allocation may **not** be async-signal-safe and thus must be prevented.

I thought async signal safe referred to a function which can be called safely within a signal handler. But the child process is not being invoked within a signal handler right? Also, assuming the child process is not being invoked within a signal handler (I am not sure if that is even a meaningful statement), is it not enough for the child process's signal handler itself to be async signal safe?

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The level of uncertainty about the state of the child process is very similar to the level of uncertainty in a signal handler. For example, if one of the other threads in the parent was in the middle of a malloc call at the time of the fork, the allocator's state is probably in a state that prevents it from working properly in the child.

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