Can we please stop using the term "low entropy" here. It is wrong and makes my head hurt. "Running out of entropy" is an urban myth. It's about the initialization state of Kernel's internal RNG. The Kernel blocks the syscall as long as it is not confident enough about its RNG. It wants to collect a decent amount of events from different sources until it considers its RNG properly seeded. Once the RNG is seeded, you can pull as many data from the RNG as you like.

It's really block_on_boot_until_kernel_rng_has_been_seeded.