Hmm, set_notify_signal() calls wake_up_state() in kernel/sched/core.c, which is not currently exported. Only by including EXPORT_SYMBOL(wake_up_state) and rebuilding vmlinux was I able to build rng-core.ko and load it successfully. That said, this patch allows 'ip link set wlan0 down' to wake a blocked process reading from /dev/hwrng, eliminating the delay as described. I'll give my sign-off with the EXPORT_SYMBOL sorted out.
