From owner-freebsd-stable  Tue Mar  5 21:42: 1 2002
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Date: Wed, 06 Mar 2002 00:41:55 -0500
To: Harry Newton <harry_newton@telinco.co.uk>
From: Mike Tancsa <mike@sentex.net>
Subject: Re: reproducible kernel panic 
Cc: freebsd-stable@FreeBSD.ORG
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Hmmm.... Is there any work around to this ?  I guess there is no way to 
limit this via login.conf ?

         ---Mike

At 11:11 PM 3/5/2002 +0000, Harry Newton wrote:
>With this:
>
>  #!/usr/local/bin/python2.2
>
>  import mmap
>  m = mmap.mmap(-1,256,mmap.MAP_ANON)
>
>  m = 1
>
>I can panic the kernel:
>
>  trap 12: page fault while in kernel mode --- supervisor read, page not
>  present
>
>  Stopped at: vm_map_clean+0x1ee: cmpl $0,0x40(%edi)
>
>I dug around a bit with the debugger, and found the fault to lie in:
>
>  /usr/src/sys/vm/vm_map.c : 1749
>
>here's the right bit ( reformatted to fit on this page )
>
>/*
>  * Note that there is absolutely no sense in writing out
>  * anonymous objects, so we track down the vnode object
>  * to write out.
>  * We invalidate (remove) all pages from the address space
>  * anyway, for semantic correctness.
>  */
>    while (object->backing_object) {
>      object = object->backing_object;
>      offset += object->backing_object_offset;
>      if (object->size < OFF_TO_IDX( offset + size))
>                         size = IDX_TO_OFF(object->size) - offset;
>                 }
>
>But: I can't be much more use, apart from noting that:
>
>  size = 4096
>  offset = -3621126458136592384
>  object = 0x0
>  object->backing_object --- can't access memory at 0x40
>
>I take it that messing round with anonymous maps shouldn't panic the
>kernel like this.
>
>Q. + Should I submit a PR ?
>    + can I supply anymore information ?
>
>
>( It was mis-keying that caused the first panic, and I've reduced it
>to the above lines of Python: I didn't set out with the above ! )
>
>- Harry
>
>--
>Harry Newton
>harry_newton at telinco.co.uk
>www.gaudeamus.telinco.co.uk/html/gpg.html
>
>To Unsubscribe: send mail to majordomo@FreeBSD.org
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Mike Tancsa,                          	          tel +1 519 651 3400
Sentex Communications,     			  mike@sentex.net
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