freebsd stable - Sep 2017 - entropy lockup

I just had a VM running in Google's cloud become totally useless, and I
tracked it down to the save-entropy operation.

Basically this process was sucking up all CPU, even when nothing else
running other than my ssh shell:

% ps axuw803
USER     PID  %CPU %MEM  VSZ  RSS TT  STAT STARTED     TIME COMMAND
operator 803 100.0  0.1 8336 2096  -  RL   08:55   48:20.14 dd
if=/dev/random of=saved-entropy.1 bs=4096 count=1


The process is unkillable, and I cannot even get the system to shut down.
That has been hanging for about 10 minutes so far, with the last output
being

System shutdown time has arrive90 second watchdSep 11 09:50:02 yertle init:
/bin/sh on /etc/rc.shutdown terminated abnormally, going to single user mode
Sep 11 09:50:47 init: some processes would not die; ps axl advised
Waiting (max 60 seconds) for system process `vnlru' to stop... done
Waiting (max 60 seconds) for system process `bufdaemon' to stop... done
Waiting (max 60 seconds) for system process `syncer' to stop...
Syncing disks, vnodes remaining... 4 4 4 4 4 4 4 timed out
2 2 2 2 2 2 2


Running FreeBSD 11.1-p1 on a 1CPU standard machine in GCE.

What's the proper recovery from this kind of lockup, or how to prevent it?
I've never encountered this on a bare metal system, or other KVM based
machines.

In all likelihood the process wasn't "hung" per-se, more likely
random
hadn't been seeded yet and as such you *can't* get 4096b of entropy out
of
it (so the process was attempting to do its job, just nothing on the
device).

The issue is basically that there are very few "good" entropy sources
in a
VM environment, and as such (particularly on a machine which is only
running SSH) there's not enough data available to seed random.

Check 'man 4 random' for some discussion.

On Tue, Sep 12, 2017 at 12:02 AM, Vick Khera <vivek at khera.org> wrote:
> I just had a VM running in Google's cloud become totally useless, and I
> tracked it down to the save-entropy operation.
>
> Basically this process was sucking up all CPU, even when nothing else
> running other than my ssh shell:
>
> % ps axuw803
> USER     PID  %CPU %MEM  VSZ  RSS TT  STAT STARTED     TIME COMMAND
> operator 803 100.0  0.1 8336 2096  -  RL   08:55   48:20.14 dd
> if=/dev/random of=saved-entropy.1 bs=4096 count=1
>
>
> The process is unkillable, and I cannot even get the system to shut down.
> That has been hanging for about 10 minutes so far, with the last output
> being
>
> System shutdown time has arrive90 second watchdSep 11 09:50:02 yertle init:
> /bin/sh on /etc/rc.shutdown terminated abnormally, going to single user
> mode
> Sep 11 09:50:47 init: some processes would not die; ps axl advised
> Waiting (max 60 seconds) for system process `vnlru' to stop... done
> Waiting (max 60 seconds) for system process `bufdaemon' to stop... done
> Waiting (max 60 seconds) for system process `syncer' to stop...
> Syncing disks, vnodes remaining... 4 4 4 4 4 4 4 timed out
> 2 2 2 2 2 2 2
>
>
> Running FreeBSD 11.1-p1 on a 1CPU standard machine in GCE.
>
> What's the proper recovery from this kind of lockup, or how to prevent
it?
> I've never encountered this on a bare metal system, or other KVM based
> machines.
> _______________________________________________
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