kern/61191: System panic on USB vs. Serial problems

[George V. Neville-Neil]

>Number:         61191
>Category:       kern
>Synopsis:       System panic on USB vs. Serial problems
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat Jan 10 19:50:15 PST 2004
>Closed-Date:
>Last-Modified:
>Originator:     George V. Neville-Neil
>Release:        FreeBSD 4.9-STABLE i386
>Organization:
Neville-Neil Consulting
>Environment:
System: FreeBSD jchurch.neville-neil.com 4.9-STABLE FreeBSD 4.9-STABLE #6: Mon Dec 22 21:14:11 PST 2003 root at jchurch.neville-neil.com:/usr/obj/usr/local/src-STABLE/src/sys/JCHURCH i386


>Description:
	I am attempting to use my desktop as a console to my 
-CURRENT target system.  To do this I have hooked COM1 on the desktop to COM1 
on the target system with a nul modem, 9 pin, cable.  While my cu session is
open on the target I get random crashes of my desktop.  I do not get a 
kernel core dump (alas) but the panic is:

Jan 10 19:17:40 jchurch /kernel: panic: clist reservation botch

This panic occurs only in one place in the kernel:

sys/kern/tty_subr.c:

cblock_alloc()
{
	struct cblock *cblockp;

	cblockp = cfreelist;
	if (cblockp == NULL)
		panic("clist reservation botch");
	cfreelist = cblockp->c_next;
	cblockp->c_next = NULL;
	cfreecount -= CBSIZE;
	return (cblockp);
}

My desktop has both the serial cable plugged into COM1 as well as a 
USB Keyboard and USB trackpad.  I know this is USB related for two reasons:

1) Someone else mentioned they were having similar problems.

2) The machine actually hangs, and only resets when I unplug the USB keyboard.

>How-To-Repeat:
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: