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    SubjectRe: Unable to handle kernel NULL pointer dereference at virtual address 00000000
    On Wed, Dec 15, 2004 at 10:29:43AM -0600, Matt Domsch wrote:
    > These messages I have gotten for years. They're debugging messages,
    > as a result of:
    > register_netdevice( alloc_divert_blk( (sees it's not an ethernet device, )
    > printk's the message )
    >
    > So I believe they're harmless.

    This is what I was thinking too. I see plenty of these messages that do
    not result in crashes.

    > > 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?
    >
    > Thanks,
    > Matt

    Fortunately we use the DL140 server pretty widely here. None of the
    non-poptop servers exhibit this problem. Every single one of them that has
    been used as a Poptop server however does exhibit this issue. It seems to
    happen more frequenly on the machines with a higher number of users
    connected.

    I have switched one of the servers (the one with the highest load) to use
    Jan Dubiec's MPPC/MPPE patches for ppp 2.4.3 and Kernel 2.6.9. We'll see
    how that goes.

    Any information I can provide or something I can do on my end to better
    trace this down?

    Ray
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