linux-kernel - Re: kernel panic about kernel unaligned access

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Date:	Thu, 5 Nov 2009 15:03:14 +0800
From:	loody <miloody@...il.com>
To:	Ben Nizette <bn@...sdigital.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: kernel panic about kernel unaligned access

hi all:

2009/10/29 Ben Nizette <bn@...sdigital.com>:
> On Tue, 2009-10-27 at 22:23 +0800, loody wrote:
>> Dear all:
>> I use kernel 2.6.18 and I get the kernel panic as below:
>
> Very old kernel, you're unlikely to get good responses.
>
>> 1. what does "Not tainted" mean?
>
> You haven't loaded a closed-source module, the system hasn't crashed
> before and a few other things.  Pretty much that your system was in good
> shape before the bug
>
>> 2. I grep the kernel and I find the above message comes from do_ade in
>> unaligned.c, If I guess correctly.
>>    but from the call trace I cannot find out who call it.
>>    who and how kernel pass the information to do_ade?
>
> No-one calls it, it's an exception handler invoked when an unaligned
> access is attempted.  Your question should be "on which assembler
> instruction is the unaligned access attempted" and you can find that out
> as below
>
>> 3. as far as i know, inode is the data structure we used to record file.
>
> Well, its a structure which holds metadata about files, yes
>
>> From what information in the inode I can find out the file name the
>> writeback_inodes try to write?
>
> Not with just this information; you'd need additional debug output, but
> even then I very much doubt that information would help you
>
>> 4. take  [<87189564>] preempt_schedule+0x68/0xac for example, what
>> does "0xac" mean?
>
> That's the symbol size. 0x68 is the offset in to preempt_schedule and
> probably more useful for you.  With that info, your vmlinux and gdb you
> can get the offending asm instruction.
>
> All that said, it's such an old kernel you're unlikely to get much help
> actually fixing the bug, you're much better off to upgrade if there's
> any chance of it.
>
>        --Ben.
I have one question.
If we use mmap in usermode to map HW registers under mips machine,
what is the proper flag I should use in mmap or open?
Since I find the problem seems come from some application try to
access registers by mmaping.
appreciate your help,
miloody
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