Re: BUG: kernel NULL pointer dereference, address: 0000000000000000

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

On Sun, 15 Mar 2026 at 00:37, Uwe Kleine-König <ukleinek@debian.org> wrote:
>
> On Sat, Jan 03, 2026 at 11:33:47AM +0000, Sudip Mukherjee wrote:
> > On Sat, Jan 03, 2026 at 12:01:19PM +0600, Paul Menzel wrote:
> > > Dear Salvatore,
> > >
> > >
> > > Thank you for the follow-up.

<snip>

>
> There are several backtraces, I looked at two of them and both trap at
> an address that corresponds to:
>
>         /*
>          * This has to be run as last thing since init_state may need other
>          * pardevice fields. -arca
>          */
> ->      port->ops->init_state(par_dev, par_dev->state);
>         if (!test_and_set_bit(PARPORT_DEVPROC_REGISTERED, &port->devflags)) {
>                 port->proc_device = par_dev;
>                 parport_device_proc_register(par_dev);
>         }
>
>
> in parport_register_dev_model(). However the trapping machine code
> doesn't match the kernel modules of the respective kernels, so that's a
> bit strange and I'm unable to tell which of the pointer dereferences
> there results in the NULL pointer exception.
>
> Maybe this is also an instance of the hardware disappearing? At least
> port->ops and pardev are non-NULL earlier in that function and all
> static initialisations of a struct parport_operations have an
> init_state() callback.

Thanks for confirming. That is also my understanding that the
underlying hardware disappeared and mentioned that in my first reply
at https://lore.kernel.org/lkml/CADVatmM_mRnkDX=hpUjbyKkZnGynxJfRSujGxm2LaWWMEL_2ew@mail.gmail.com/#t


-- 
Regards
Sudip