kern/39536: bufq related problem when writing DVDR and DVDRWs

[lars.nordlund%hem.utfors.se@localhost]

>Number:         39536
>Category:       kern
>Synopsis:       bufq related problem when writing DVDR and DVDRWs
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Sep 13 20:55:00 +0000 2008
>Originator:     Lars Nordlund
>Release:        4.99.72
>Organization:
NA
>Environment:
NetBSD laphroaig 4.99.72 NetBSD 4.99.72 (LAPHROAIG) #1: Sat Sep 13 13:55:10 
CEST 2008  
lars@laphroaig:/home/lars/tmp/current-obj_amd64/sys/arch/amd64/compile/LAPHROAIG
 amd64
>Description:
See this mail thread for all the background information:

http://arkiv.netbsd.se/?ml=netbsd-current-users&a=2008-09&t=8378989

I am using growisofs from pkgsrc to trigger the fault. The crashes look a bit 
different each time, but they are all buf related. See these ddb backtraces as 
examples:

http://www.ludd.ltu.se/~nordlund/lockdebug_lookup.jpg

http://www.ludd.ltu.se/~nordlund/bufq_disksort_get.jpg
>How-To-Repeat:
Use growisofs to write DVDR or DVD-RW. I get the fault more frequently when 
AHCI is turned off for the delivering hard disk controller (hard disk 
containing the ISO file on goes from a 50MiB/s write-speed-disk to a 5-10MiB/s 
write-speed-disk).
>Fix:
Turn on DIAGNOSTIC.

or..

Turn on QUEUEDEBUG

I can not repeat the hang with either of these options turned on.