linux-kernel - Re: [2.6.26] kobject_add_internal failed for 2:0 with -EEXIST / unable to handle kernel NULL pointer dereference in sysfs_create

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Date:	Mon, 03 Nov 2008 12:55:35 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Folkert van Heusden <folkert@...heusden.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [2.6.26] kobject_add_internal failed for 2:0 with -EEXIST /
 unable to handle kernel NULL pointer dereference in sysfs_create_link

On Mon, 2008-11-03 at 12:53 +0100, Kay Sievers wrote:
> On Fri, Oct 31, 2008 at 10:28, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > On Fri, 2008-10-31 at 00:23 +0100, Kay Sievers wrote:
> >
> >> Peter, it looks like bdi does not work for devices which share a single queue.
> >> If I add:
> >>   --- a/mm/backing-dev.c
> >>  +++ b/mm/backing-dev.c
> >>   @@ -184,6 +184,8 @@ int bdi_register(struct backing_dev_info *bdi,
> >> struct device *parent,
> >>                   goto exit;
> >>           }
> >>
> >>   +       printk("XXXXXXX old bdidev is %p\n", bdi->dev);
> >>   +       printk("XXXXXXX new bdidev is %p\n", dev);
> >>           bdi->dev = dev;
> >>           bdi_debug_register(bdi, dev_name(dev));
> >>
> >> I get:
> >>   $ modprobe floppy
> >>   Floppy drive(s): fd0 is 1.44M, fd1 is 1.44M
> >>   FDC 0 is a S82078B
> >>   XXXXXXX old bdidev is 0000000000000000
> >>   XXXXXXX new bdidev is ffff88001f20cd10
> >>   XXXXXXX old bdidev is ffff88001f20cd10
> >>   XXXXXXX new bdidev is ffff88001f20de30
> >>
> >> which very much looks like bdi will not remove any earlier registered
> >> device, only the last one, right?
> >
> > Sharing a bdi is odd to begin with, let me poke at this a little.
> 
> Yeah, it's odd, but I'm not sure if you want to touch floppy.c. :)
> Any objection to this patch, until you possible fix it differently?
>   http://marc.info/?l=linux-kernel&m=122541569310798&w=4

Non at all, touching floppy.c is dangerous, folks might assume you know
something about it ;-)

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