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From: Peter Dufault <dufault@hda.com>
Message-Id: <199512190248.VAA18815@hda.com>
Subject: Re: Problem with FreeBSD 2.1.0-RELEASE
To: gibbs@freefall.freebsd.org (Justin T. Gibbs)
Date: Mon, 18 Dec 1995 21:48:58 -0500 (EST)
Cc: m.sapsed@bangor.ac.uk, hm@hcs.de, freebsd-bugs@freebsd.org
In-Reply-To: <199512181948.LAA15318@freefall.freebsd.org> from "Justin T. Gibbs" at Dec 18, 95 11:48:36 am
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> >This is probably your problem.  I found this in cd.c:
> >
> >#define CDUNIT(DEV)      ((minor(DEV)&0xF8) >> 3)    /* 5 bit unit */
> >
> >It should be:
> >
> >#define CDUNIT(DEV)	((minor(DEV) >> 11) | ((minor(DEV)&0xF8) >> 3))
> >
> >This is probably a general problem in the SCSI code.
> 
> Actually, this only becomes a factor with 32 cds.  Hmmm.  Can you
> put ddb in your kernel and get a traceback from the panic?

This is certainly the same problem that Hellmuth and others
have been having with CD-ROM changers.  Hellmuth sent me the changer so I
want to find some time to track it down soon.  I saved some mail from
him that says it takes place here:

> Fatal trap 12: page fault while in kernel mode
> Fault virtual address              = 0x60
> Fault code                         = supervisor read, page not present
> Instruction pointer                = 0x8:0xf01250ac
> Code segment                       = base 0x0 limit 0xfffff type 0x1b
>                                    = DPL 0, pres 1, def 321, gran 1
> Processor eflags                   = interrupt enabled, resume, IOPL = 0
> Current process                    = 470 (iozone)
> Interrupt mask                     = bio
> Kernel: type 12 trap, code = 0
> Stopped at _incore+0x48: cmpl %esi, 0x48(%ebx)

I believe this is here in kern/vfs_bio.c:

>	int s = splbio();
>
>	bh = BUFHASH(vp, blkno);
>	bp = bh->lh_first;
>
>	/* Search hash chain */
>	while (bp) {

where we go indirect on that bp.

--
Peter Dufault               Real Time Machine Control and Simulation
HD Associates, Inc.         Voice: 508 433 6936
dufault@hda.com             Fax:   508 433 5267