[$] Fixing getrandom()
A report of
a boot hang in the 5.3 series has led to an enormous, somewhat contentious
thread on the linux-kernel mailing list. The proximate cause was some changes that made the
ext4 filesystem do less I/O early in the boot phase, incidentally causing
fewer interrupts, but the
underlying issue was the getrandom()
system call, which was blocking until the /dev/urandom pool
was initialized—as designed. Since the system in question was not
gathering enough entropy due to the lack of unpredictable interrupt
timings, that would hang more or less forever. That has called into
question the design and implementation of getrandom().