Haines Brown <haines@???> writes:
> I installed 64bit jessie on a new HDD, and initially used the 3.16.0
> kernel. Then I installed the 4.50 kernel and ran into trouble.
>

>   kernel:[25090.816205] NMI watchdog: BUG: soft lockup - CPU #7
>       stuck for 22!s
>         [colord-sane:20969]

>
> This message is displayed every few seconds in whatever happens to have
> the focus and is accompanied with a beep. The keyboard and mouse
> hang so that I must do a hot reboot.
>
> Is this in fact a kernel bug?

The message comes from the NMI watchdog in the kernel and indicates a
possibly bug in some application. The comment above the statement
printing this message may be helpful here:

        /* check for a softlockup
         * This is done by making sure a high priority task is
         * being scheduled.  The task touches the watchdog to
         * indicate it is getting cpu time.  If it hasn't then
         * this is a good indication some task is hogging the cpu
         */

If this feature is enabled, there's a dedicated kernel thread running on
each CPU (named watchdog/<number>) which will reset the watchdog timeout
whenever it gets CPU time to do so. The message is printed of this
thread didn't have a chance to run during the checking interval because
another task ate all available CPU time. The stack backtrace & other
information printed together with this message should provide more
information about this other task.

NB: I've been running 4.5.0 ever since it was released (the upstream
kernel).