getrandom() before forking daemon is blocking init system

[Axel Burri]

Hello

When booting from a slow machine, I can observe dovecot blocking the
whole boot process. I traced it down to the getrandom() system call in
lib/randgen.c, which blocks until the random number generator is
initialized (dmesg "random: crng init done"). This can take up to three
minutes (!) on my machine, as there is not much entropy available (no
hardware RNG, network VPN is also waiting for random).

Unfortunately dovecot calls getrandom() before forking a daemon, which
as a consequence blocks the whole init process (OpenRC on Gentoo Linux).

I believe this behavior has changed in kernel 4.14:

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v4.14.40&id=6e513bc20ca63f594632eca4e1968791240b8f18

Quoting getrandom(2):
"If the urandom source has not yet been initialized, then getrandom()
will block, unless GRND_NONBLOCK is specified in flags."


Dovecot: 2.3.4.1 (f79e8e7e4)

Linux: 4.19.26-gentoo #2 SMP Thu Feb 28 20:30:23 CET 2019 x86_64 AMD
G-T40E Processor AuthenticAMD GNU/Linux


Regards,

Axel