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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Message-ID: <ac3eb2510811030353i72a2a5f6i8869addea1057cfa@mail.gmail.com>
Date:	Mon, 3 Nov 2008 12:53:03 +0100
From:	"Kay Sievers" <kay.sievers@...y.org>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
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 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

Kay
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