Bug#854182: Solved
An update after some testing.
The bug persists in the latest stable kernel, linux-image-4.9.30-2.
It is solved by compiling the debian kernel with CONFIG_X86_ACPI_CPUFREQ=y. Just to be sure, I compiled the latest debian kernel source with the default CONFIG_X86_ACPI_CPUFREQ=m option and failed exactly the same way as with the binary kernel.
While troubleshooting I 've found some suboptimals workarounds, they might be useful to someone.
Boot succeeds with any of these kernel parameters:
acpi=off
nolapic
idle=poll
processor.max_cstate=2 (or 0 or 1, but NOT 3)
Strangely, the ac power trick (unplugged during initramfs) doesn't work anymore.
Anyway, my non-technical, non-expert view is that acpi-cpufreq when built as a module doesn't like transitioning from c2 to c3 state during initramfs loading.
Hope it helps someone.
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