kern/38762: panic: vwakeup: neg numoutput

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         38762
>Category:       kern
>Synopsis:       panic: vwakeup: neg numoutput
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon May 26 19:05:04 +0000 2008
>Originator:     Andreas Gustafsson
>Release:        NetBSD 4.99.62 as of 20080516-1010 EET
>Organization:
>Environment:
System: NetBSD 4.99.62
Architecture: i386
Machine: i386
>Description:

NetBSD-current will panic if I attach a USB mass storage device with
an FFS file system to a USB 2.0 port, mount it, and write a file to
it.  The panic message looks like

  panic: vwakeup: neg numoutput, vp 0xcccb274c

I have reproduced this on three different i386 machines using two
different USB mass storage devices (one flash memory stick and one
hard disk).

For a screenshot and DDB backtrace, see

  http://www.gson.org/netbsd/bugs/negnum/1.jpg
  http://www.gson.org/netbsd/bugs/negnum/2.jpg
  http://www.gson.org/netbsd/bugs/negnum/3.jpg

The file system used in this test was freshly fsck'd.

>How-To-Repeat:

Create a FFS file system on a USB mass storage device.  Attach it to a
USB 2.0 (EHCI) port; let's assume it attaches as sd0.  Enter the
commands

  mount /dev/sd0a /mnt
  echo foo >/mnt/bar

If this doesn't panic, try

  umount /dev/sd0a

>Fix: