Your patch did not resolve the kernel panic.
I think, we should check knlist_clear() before knlist_destroy().
When a device is lost suddenly, usb_dev notify to a process in
usb_fifo_close() and then calls knlist_destroy(). knlist_destroy()
clears knlist->kn_lock and knlist->kn_unlock.

But, the process that is notified will start over kqueue_scan() after
knlist_destroy(). And, in KN_LIST_LOCK(kn), the context will call NULL
function (kn->knlist->kn_lock).

 Kohji Okuno

> On 02/27/14 11:39, Kohji Okuno wrote:
>> Hi HPS and John-Mark,
>> After I changed as the following, the kernel panic does not happen.
>> What do you think about this change?
>> +       knlist_clear(&f->selinfo.si_note, 0);
>>          knlist_destroy(&f->selinfo.si_note);
>> Regards,
>>   Kohji Okuno
> Can you try the attached patch instead?
> --HPS
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