Date: Mon, 18 Dec 1995 19:42:33 -0800 From: David Greenman <davidg@Root.COM> To: Peter Dufault <dufault@hda.com> Cc: gibbs@freefall.freebsd.org (Justin T. Gibbs), m.sapsed@bangor.ac.uk, hm@hcs.de, freebsd-bugs@freebsd.org Subject: Re: Problem with FreeBSD 2.1.0-RELEASE Message-ID: <199512190342.TAA02913@corbin.Root.COM> In-Reply-To: Your message of "Mon, 18 Dec 95 21:48:58 EST." <199512190248.VAA18815@hda.com>
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>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
...
>> 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.
This is a "can't happen" panic. It can only happen if the CPU executes the
instructions incorrectly. The assembly code is:
...
movl _bufhashtbl(,%eax,4),%ebx
testl %ebx,%ebx <- exit if bp is NULL
je L326
movl %edx,%ecx
notl %ecx
movl %ecx,-4(%ebp)
.align 2,0x90
L327:
cmpl %esi,72(%ebx) <- failing here
jne L328
cmpl %edi,88(%ebx)
jne L328
movl 36(%ebx),%eax
testb $32,%ah
jne L328
movl %edx,_cpl
movl _ipending,%eax
testl %eax,-4(%ebp)
je L329
call _splz
L329:
movl %ebx,%eax
jmp L334
.align 2,0x90
L328:
movl (%ebx),%ebx
testl %ebx,%ebx <- jump if bp *not* NULL
jne L327
L326:
movl %edx,_cpl
notl %edx
movl _ipending,%eax
testl %edx,%eax
je L332
call _splz
L332:
xorl %eax,%eax
L334:
leal -16(%ebp),%esp
popl %ebx
popl %esi
popl %edi
leave
ret
The only other possibility is that incore() isn't actually being called at
all and the CPU ended up here because of some weird stack corruption or
bogus function pointer or something. ...This seems unlikely.
-DG
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