linux-kernel - Re: 2.6.19-rc5-mm2 (end earlier): WARNING at lib/kobject.c:172 kobject

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Date:	Wed, 22 Nov 2006 16:39:35 -0800
From:	Greg KH <greg@...ah.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.19-rc5-mm2 (end earlier): WARNING at lib/kobject.c:172 kobject_init() on resume from disk

On Wed, Nov 22, 2006 at 01:44:06PM -0800, Andrew Morton wrote:
> On Wed, 22 Nov 2006 22:07:06 +0100
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> > Hi,
> > 
> > I get similar traces on every resume from disk on SMP systems:
> > 
> > WARNING at lib/kobject.c:172 kobject_init()
> > 
> > Call Trace:
> >  [<ffffffff80265559>] dump_trace+0xaa/0x3fd
> >  [<ffffffff802658e8>] show_trace+0x3c/0x52
> >  [<ffffffff80265913>] dump_stack+0x15/0x17
> >  [<ffffffff8031c1ad>] kobject_init+0x3f/0x8a
> >  [<ffffffff8031c298>] kobject_register+0x1a/0x3e
> >  [<ffffffff8038e5b4>] sysdev_register+0x5f/0xec
> >  [<ffffffff8026af39>] mce_create_device+0x79/0x103
> >  [<ffffffff8026afed>] mce_cpu_callback+0x2a/0xbd
> >  [<ffffffff8026112f>] notifier_call_chain+0x29/0x3e
> >  [<ffffffff8028e809>] raw_notifier_call_chain+0x9/0xb
> >  [<ffffffff80299f18>] _cpu_up+0xc2/0xd5
> >  [<ffffffff80299f56>] cpu_up+0x2b/0x42
> >  [<ffffffff80299fbb>] enable_nonboot_cpus+0x4e/0x9b
> >  [<ffffffff802a35da>] snapshot_ioctl+0x1a0/0x5d2
> >  [<ffffffff8023d9cd>] do_ioctl+0x5e/0x77
> >  [<ffffffff8022d785>] vfs_ioctl+0x256/0x273
> >  [<ffffffff8024770b>] sys_ioctl+0x5f/0x82
> >  [<ffffffff8025811e>] system_call+0x7e/0x83
> > DWARF2 unwinder stuck at system_call+0x7e/0x83
> > Leftover inexact backtrace:
> > 
> > False positive?
> > 
> 
> Don't know.  The changelog in
> http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/gregkh-01-driver/kobject-warn.patch
> is pretty pathetic.

Heh, I would think that it's a big "obvious", oh well.

There are 2 changes in this patch.

First one is to ensure that the kobject is properly initialized _before_
kobject_init() is called.  Yeah, seems funny, right?  Turns out this has
caught a lot of issues where kobject_init() is called twice on the same
object, not a good thing at all.

And this looks like that is exactly what is happening here, as you
mention:

> Perhaps mce_remove_device() isn't being called.

That's probably the issue.

The second change in that patch tries to enforce the "everything needs a
release() function" rule for kobjects, but it turns out, a lot of static
kobjects trigger this inproperly (struct bus and friends), so that can't
go to mainline, and it only shows up if you enable CONFIG_KOBJECT_DEBUG.

Hope this helps explain things, I'll go off and edit the text there to
make it clearer.

thanks,

greg k-h
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