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    SubjectRe: Unable to handle kernel NULL pointer dereference at virtual address 00000000
    On Tue, Dec 14, 2004 at 05:32:28PM -0800, Ray Van Dolson wrote:
    > Hoping someone can shed some light on this, or help me out in narrowing the
    > problem down.
    > Our servers exhibit these error messages (at bottom) off and on and
    > eventually appears to lead to system instability. I guess the three
    > possibilities are that this is either a) a hardware problem, b) a problem
    > with poptop, pppd or the mppe modules, or c) a problem with the kernel
    > This happens on every single one of our DL140's, so if it's a hardware
    > problem, then it is widespread on this platform.
    > If it's a problem with poptop, pppd or mppe modules I'd at least like to be
    > able to give some evidence to that effect...
    > If it's c, I'm hoping someone here can give some suggestions on how to
    > resolve this. :-) Please let me know if I can provide further information.
    > I have a box on which this happens fairly regularly, so I can reproduce it
    > pretty easily.
    > Thanks in advance!
    > System Specs:
    > HP DL140
    > Dual 2.4GHz P4 Xeon w/ Hyperthreading
    > Fedora Core 2
    > 2.6.9 kernel (static compile, downloaded from with the
    > following patches):
    > -
    > This fixes an oops I was getting in mm/prio_tree.c
    > -
    > This provides MPPE support for clients connecting via PoPToP 1.2.1.
    > Intel E100 Pro Dual Port NIC (Using built-in e100 driver).
    > Onboard Broadcom BCM5700 Gigabit NIC's are *not* in use (no driver support
    > compiled in)
    > Software:
    > Poptop 1.2.1
    > PPP 2.4.3
    > Kernel config:
    > lspci output:

    > <7>divert: not allocating divert_blk for non-ethernet device ppp440

    These messages I have gotten for years. They're debugging messages,
    as a result of:
    (sees it's not an ethernet device, printk's the message)

    So I believe they're harmless.

    > ksymoops output of problem:
    > Unable to handle kernel NULL pointer dereference
    > 00000000
    > *pde = 00000000
    > Oops: 0000 [#1]
    > CPU: 2
    > EIP: 0060:[<00000000>] Not tainted VLI
    > Using defaults from ksymoops -t elf32-i386 -a i386
    > EFLAGS: 00010286 (2.6.9)
    > eax: ed13b000 ebx: d1d0a000 ecx: c029e9de edx: f795ef40
    > esi: d1d0a000 edi: 00000000 ebp: e2f30080 esp: d2b0dea0
    > ds: 007b es: 007b ss: 0068
    > Stack: c02a205a ed13b000 00000000 c02a122c d1d0a000 13208a2e c040956f d1d0a000
    > d1d0a00c e2f30080 00000000 c029cda9 d1d0a000 e2f30080 00000000 c01552cd
    > e2f30080 00000010 00000004 00000004 c0166aa0 e2f30080 00000000 00000000
    > Call Trace:
    > [<c02a205a>] pty_chars_in_buffer+0x2c/0x49
    > [<c02a122c>] normal_poll+0xed/0x150
    > [<c040956f>] schedule_timeout+0x75/0xbf
    > [<c029cda9>] tty_poll+0xa0/0xb0
    > [<c01552cd>] fget+0x49/0x5e
    > [<c0166aa0>] do_select+0x269/0x2c6
    > [<c0166691>] __pollwait+0x0/0xc7
    > [<c0166dd5>] sys_select+0x2b3/0x4c6
    > [<c0105971>] sysenter_past_esp+0x52/0x71
    > Code: Bad EIP value.

    It looks like pty_chars_in_buffer() dereferenced a NULL function
    pointer, but I don't see how that can be, the one deference is tested
    for NULL before doing so.

    I can't rule out the ppp_mppe code, but I haven't seen this crash
    before myself. Does this happen on simlar systems that aren't running poptop?


    Matt Domsch
    Sr. Software Engineer, Lead Engineer
    Dell Linux Solutions &
    Linux on Dell mailing lists @
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