Re: kern/38762: panic: vwakeup: neg numoutput

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

The following reply was made to PR kern/38762; it has been noted by GNATS.

From: gson%gson.org@localhost (Andreas Gustafsson)
To: Antti Kantee <pooka%cs.hut.fi@localhost>
Cc: gnats-bugs%NetBSD.org@localhost
Subject: Re: kern/38762: panic: vwakeup: neg numoutput
Date: Fri, 22 Aug 2008 15:23:34 +0300

 Antti Kantee wrote:
 > Hmm, sounds suspicious.  Are you *sure* you're trying the exact same
 > kernel, machine, usb stick, etc?
 
 The netboot kernel configuration is GENERIC; the live CD kernel
 configuration is LIVECD, with the following contents:
 
    include "GENERIC"
    no config netbsd
    config netbsd root on cd0a type cd9660 dumps on none
    options INCLUDE_CONFIG_FILE
 
 Same physical machine, same USB stick.
 
 > Seems like the data flush triggers the problem, as the echo command has
 > returned already.  So I'm guessing "sync" is enough instead of unmount.
 
 You are correct.  The following sequence of commands triggered the
 panic when booted from the live CD (and if anyone wants to try it,
 please note that it will wipe out the entire contents of your hard
 disk):
 
    dd if=/dev/zero bs=1m of=/dev/rwd0d
    newfs /dev/rwd0a
    mount /dev/wd0a /mnt
    echo foo >/mnt/bar
    sync
 
 > Can you do "show vnode" for the problematic vnode?
 
 Yes.  This is transcribed by hand from a VGA console, so there may be
 typos:
 
    panic: wvakeup: neg numoutput, vp 0xcc10c750
    Stopped in pid 0.4 (system) at  netbsd:breakpoint+0x4:  popl    %ebp
    db{0}> show vnode 0xcc10c750
    OBJECT 0xcc10c750: locked=1, pgops=0xc07cfca0, npages=0, refs=3
 
    VNODE flags 24010<MPSAFER,ONWORKLST,LAYER>
    mp 0xcbd19000 numoutput -1 size 0x0 writesize 0x0
    data 0xcbe4044c writecount 0 holdcnt 4
    tag VT_NULL(9) type VBLK(3) mount 0xcbd19000 typedata 0xcbe40460
    v_lock 0xcc10c7dc v_unlock 0xcbe70b1c
 
 > If you have puffs/rump available, can you see if it tickles the problem
 > also?  rump_ffs /dev/rsd0a /mnt ; echo foo > /mnt/bar ; sync
 
 I will try that after -current has finished building.
 -- 
 Andreas Gustafsson, gson%gson.org@localhost