netdev - Re: [BRIDGE] warning message when add an interface to bridge

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Message-ID: <m1odd4tlay.fsf@ebiederm.dsl.xmission.com>
Date:	Wed, 05 Dec 2007 23:00:05 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	"Chung-Chi Lo" <linolo@...il.com>, netdev@...r.kernel.org
Subject: Re: [BRIDGE] warning message when add an interface to bridge

Stephen Hemminger <shemminger@...ux-foundation.org> writes:

> On Wed, 5 Dec 2007 10:44:17 +0800
> "Chung-Chi Lo" <linolo@...il.com> wrote:
>
>> My kernel is Linxu 2.6.22.1. SYSFS is off.
>> When adding an interface to bridge, console will show WARNING message.
>> If turn SYSFS to on, then the WARNING message is gone.
>> Any suggestion how to debug this problem? Thanks.
>> 
>> # ifconfig eth0 0.0.0.0
>> eth0: starting interface.
>> # brctl addbr br0
>> # brctl addif br0 eth0
>> WARNING: at lib/kref.c:33 kref_get()
>> Call Trace:
>> [<80027844>] dump_stack+0x8/0x38
>> [<8011f348>] kref_get+0xdc/0xe4
>> [<8011ee20>] kobject_get+0x20/0x34
>> [<8011e910>] kobject_shadow_add+0x5c/0x170
>> [<8011ea34>] kobject_add+0x10/0x20
>> [<8020aac0>] br_add_if+0xb4/0x1b4
>> [<8020b354>] add_del_if+0x5c/0x118
>> [<8020bcc4>] br_dev_ioctl+0x6c/0x88
>> [<80182edc>] dev_ifsioc+0x334/0x3c0
>> [<80183184>] dev_ioctl+0x21c/0x2ec
>> [<8016f76c>] sock_ioctl+0x130/0x2e4
>> [<800b3b2c>] do_ioctl+0x6c/0x84
>> [<800b3d40>] vfs_ioctl+0x80/0x248
>> [<800b3f58>] sys_ioctl+0x50/0x98
>> [<8002a8a8>] stack_done+0x20/0x3c
>> --
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>
> This is an an artifact of the kobject_shadow code which was reverted in later
> kernels.
> It is gone in 2.6.23

I don't think it was the kobject_shadow, but rather we didn't initialize the kref
or something like that in net/core/dev.c

I believe commit 8b41d1887db718be9a2cd9e18c58ce25a4c7fd93 was the fix.

Disabling sysfs can be a fun exercise in finding corner case bugs right now.

Eric

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