Re: 7.0-CURRENT Hang

I identified the problem (see my original discussion about this in attached 
the email below).

On the Pentium P54C model (that's an old 120 MHz Pentium I use as a 4.x, 
5.x, and 7.x ports build testbed) the CPUID instruction when called with AL 
= 0, CPUID returns EAX = EBX = ECX = EDX = 0. The code fragment in 
identcpu.c below results in "rounds" becoming 0xffffffff.

	do_cpuid(0x2, regs);
	rounds = (regs[0] & 0xff) - 1;

The subsequent loop of the following will loop virtually for ever (it takes 
forever tor this machine to count down from 0xffffffff performing a very 
great many calls to get_INTEL_TLB in the process, virtually hanging the 
machine in the process.

	while (rounds > 0) {
		[... code ...]
		rounds--;
	}

To resolve my problem I cobbled up the following patch to identcpu.c:

--- sys/i386/i386/identcpu.c.orig	Thu Feb  2 04:44:09 2006
+++ sys/i386/i386/identcpu.c	Mon Feb  6 18:47:16 2006
_at__at_ -1237,7 +1237,7 _at__at_
 
 	do_cpuid(0x2, regs);
 
-	rounds = (regs[0] & 0xff) - 1;
+	rounds = (regs[0] & 0xff);
 
 	for (regnum = 0; regnum <= 3; ++regnum) {
 		if ((regs[regnum] & (1<<31)) == 0) {
_at__at_ -1249,7 +1249,7 _at__at_
 		}
 	}
 
-	while (rounds > 0) {
+	while (rounds > 1) {
 		do_cpuid(0x2, regs);
 
 		for (regnum = 0; regnum <= 3; ++regnum) {
_at__at_ -1452,7 +1452,7 _at__at_
 	u_int nwaycode;
 
 	do_cpuid(0x2, regs);
-	rounds = (regs[0] & 0xff) - 1;
+	rounds = (regs[0] & 0xff);
 
 	for (regnum = 0; regnum <= 3; ++regnum) {
 		if ((regs[regnum] & (1<<31)) == 0) {
_at__at_ -1468,7 +1468,7 _at__at_
 		}
 	}
 
-	while (rounds > 0) {
+	while (rounds > 1) {
 		do_cpuid(0x2, regs);
 
 		for (regnum = 0; regnum <= 3; ++regnum) {

It fixes the hang.


Cheers,
Cy Schubert <Cy.Schubert_at_komquats.com>
Web:  http://www.komquats.com and http://www.bcbodybuilder.com
FreeBSD UNIX:  <cy_at_FreeBSD.org>   Web:  http://www.FreeBSD.org
BC Government:  <Cy.Schubert_at_gov.bc.ca>

    "Lift long enough and I believe arrogance is replaced by
    humility and fear by courage and selfishness by generosity
    and rudeness by compassion and caring."
        -- Dave Draper

In message <200601292252.k0TMqAGJ031333_at_cwsys.cwsent.com>, Cy Schubert 
writes:
> I'm experiencing the following hang on my -CURRENT testbed (which also 
> serves as a 4.11, 5.4, and 6.0 testbed). Only under 7.0-CURRENT does it 
> hang during boot using a stock out of the box GENERIC kernel. The machine 
> is an old P120. Any ideas?
> 
> OK include /boot/cwtest/foobar
> |
> 
> cwtest.foobar loader file selected
> unload complete
> currdev set to disk2s1a:
> /boot/kernel/kernel text=0x4e15c4 data=0x84900+0xa026c 
> syms=[0x4+0x67ea0+0x4+0x7f4ff]
> new kernel has been loaded
> 
> OK boot -s
> GDB: no debug ports present
> KDB: debugger backends: ddb
> KDB: current backend: ddb
> Copyright (c) 1992-2006 The FreeBSD Project.
> Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
>         The Regents of the University of California. All rights reserved.
> FreeBSD 7.0-CURRENT #0: Fri Jan 27 13:49:18 PST 2006
>     root_at_cwsys:/export/obj/opt/src/cvs-current/src/sys/GENERIC
> WARNING: WITNESS option enabled, expect reduced performance.
> 
> At this point I need to reset the machine.
> 
> 
> 
> Cheers,
> Cy Schubert <Cy.Schubert_at_komquats.com>
> Web:  http://www.komquats.com and http://www.bcbodybuilder.com
> FreeBSD UNIX:  <cy_at_FreeBSD.org>   Web:  http://www.FreeBSD.org
> BC Government:  <Cy.Schubert_at_gov.bc.ca>
> 
>     "Lift long enough and I believe arrogance is replaced by
>     humility and fear by courage and selfishness by generosity
>     and rudeness by compassion and caring."
>         -- Dave Draper
> 
> 
> 
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