PSA: If you run -current, beware!

[Ian Lepore]

On Tue, 2015-02-03 at 13:33 -0800, Peter Wemm wrote:
> Sometime in the Dec 10th through Jan 7th timeframe a timing bug has been 
> introduced to 11.x/head/-current.    With HZ=1000 (the default for bare metal, 
> not for a vm); the clocks stop just after 24 days of uptime.  This means 
> things like cron, sleep, timeouts etc stop working.  TCP/IP won't time out or 
> retransmit, etc etc.  It can get ugly.
> 
> The problem is NOT in 10.x/-stable.
> 
> We hit this in the freebsd.org cluster, the builds that we used are:
> FreeBSD 11.0-CURRENT #0 r275684: Wed Dec 10 20:38:43 UTC 2014 - fine
> FreeBSD 11.0-CURRENT #0 r276779: Wed Jan  7 18:47:09 UTC 2015 - broken
> 
> If you are running -current in a situation where it'll accumulate uptime, you 
> may want to take precautions.  A reboot prior to 24 days uptime (as horrible a 
> workaround as that is) will avoid it.
> 
> Yes, this is being worked on.

FWIW, 24.8 days is the point at which an int32_t variable counting ticks
at 1khz rolls over from positive to negative numbers.

-- Ian