USB locks up system -- WAS Re: shutdown or acpi problem

[Ian Lepore]

On Sun, 2014-11-16 at 18:23 +0000, Mark R V Murray wrote:
> > On 16 Nov 2014, at 18:21, Ian Lepore <ian at FreeBSD.org> wrote:
> > 
> > On Sun, 2014-11-16 at 18:17 +0000, Mark R V Murray wrote:
> >>> On 16 Nov 2014, at 17:51, Steve Kargl <sgk at troutmask.apl.washington.edu> wrote:
> >>> 
> >>> Is there a 'random: device_detach():' missing between the 'umass0'
> >>> and 'da0' messages in the last 4 lines.
> >> 
> >> No. At attach time, the RNG grabs some probe entropy. At detach time it does nothing.
> >> 
> >> M
> > 
> > And yet... Steve has gathered evidence that the system bricks when a
> > device is detached with the new entropy-gathering code and doesn't do so
> > prior to that code.  What else is the new code doing around detach time?
> 
> Nothing, except possibly harvesting interrupt entropy. I’ll promise to be
> astonished if this is other-than-harmless.
> 
> I’d be more suspicious of the harvester thread, but I still can’t see how
> its hurting :-(
> 
> M

The point I'm trying to make here is that you trimmed away the important
part of the prior messages and replied only to the part where Steve's
debugging efforts were somewhat speculating.  The non-speculative part
was where he bisected the failure to an exact commit:

> > > The problem is caused
> > > by r273872.  This is the recent random device patch.  I have no
> > > idea why removing a usb device would cause the system to lock
> > > up other than random is probably trying to harvest some entropy.

-- Ian