Yet another crash in FreeBSD 5.1

[Greg 'groggy' Lehey]

On Saturday,  2 August 2003 at  2:11:24 -0700, Terry Lambert wrote:
> Eivind Olsen wrote:
>> Can anyone suggest what I do next to find out about this crash?
>
>> Fatal trap 12: page fault while in kernel mode
>> fault virtual address   = 0x14
>
> Dereference of NULL pointer; reference is for element at offset
> 0x14 in some structure; this is the equivalent of 5 32 bit ints
> or pointers into the structure.
>
>> db> trace
>> g_dev_strategy(c2156024,c2153800,0,cfb528d0,c2099eca) at g_dev_strategy+0x29
>> launch_requests(c299bf00,0,10000,ffffffff,47) at launch_requests+0x448
>> vinumstart(c5ada2d0,0,c22ab000,cfb5294c,c02e5bc6) at vinumstart+0x2b2
>
> gdb -k kernel.debug
> (gdb) list *(g_dev_strategy+29)
> [ ... ]
> (gdb) list *(launch_requests+448)
> [ ... ]
> (gdb) list *(vinumstart+2b2)
> [ ... ]
>
> Will give you the exact source lines involved, assuming you
> built a debug kernel.
>
> You don't actually need a crash dump to debug a stack traceback.

Great!  So you know the answer?  Please submit a patch.

Seriously, this is nonsense.  Yes, it's a null pointer dereference.
What?  Why?  How do you fix it?  Finding the first step doesn't solve
the problem.

Greg
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