linux-kernel - Re: [dm-devel] Re: dm: sysfs add empty release function to avoid debug warning

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Message-ID: <20091216174632.GA12473@kroah.com>
Date:	Wed, 16 Dec 2009 09:46:32 -0800
From:	Greg KH <greg@...ah.com>
To:	Zdenek Kabelac <zkabelac@...hat.com>
Cc:	device-mapper development <dm-devel@...hat.com>,
	Milan Broz <mbroz@...hat.com>, linux-kernel@...r.kernel.org,
	Alasdair G Kergon <agk@...hat.com>
Subject: Re: [dm-devel] Re: dm: sysfs add empty release function to avoid
 debug	warning

On Wed, Dec 16, 2009 at 05:32:21PM +0100, Zdenek Kabelac wrote:
> Dne 16.12.2009 14:45, Greg KH napsal(a):
> > On Wed, Dec 16, 2009 at 10:44:41AM +0100, Milan Broz wrote:
> >> On 12/16/2009 01:47 AM, Greg KH wrote:
> >>> On Tue, Dec 15, 2009 at 05:35:08PM +0000, James Bottomley wrote:
> >>>> commit: d2bb7df8cac647b92f51fb84ae735771e7adbfa7
> >>>> From: Milan Broz <mbroz@...hat.com>
> >>>> Date: Thu, 10 Dec 2009 23:51:53 +0000
> >>>> Subject: [PATCH] dm: sysfs add empty release function to avoid debug warning
> >>>>
> >>>> This patch just removes an unnecessary warning:
> >>>>  kobject: 'dm': does not have a release() function,
> >>>>  it is broken and must be fixed.
> >>>>
> >>>> The kobject is embedded in mapped device struct, so
> >>>> code does not need to release memory explicitly here.
> >>>
> >>
> >>> Please, this is totally and completly wrong.  And if you feel that it is
> >>> needed, then your design is wrong and it needs to be fixed.
> >>
> >> There are several places in kernel, where kobject have not defined release
> >> method. Yes, something is wrong here.
> > 
> > Where are those instances, becides the use of static kobjects, which is
> > being worked on?
> > 
> > That still does not make this change acceptable, it is incorrect.
> > 
> >> So quietly ignoring warning is ok? Why is not there BUG_ON(!release) then?
> > 
> > I was trying to be nice and not crash your machine and give you the
> > opportunity to fix it easily.
> > 
> >> The sysfs attributes here just represents attributes of block device object,
> >> this device is always removed before release here is called.
> > 
> > Then why use a kobject at all?  Your reference counting will be all
> > wrong if you use it incorrectly like this.
> > 
> >> So if there is preferred to do another alloc/free, no problem.
> > 
> > Please do.
> > 
> > Also, with the addition of this patch, your comments for the kobject are
> > now incorrect as well.
> > 
> 
> Here is list of just some errors I get on my 2.6.32 linux kernel.
> (error message itself is removed)
> Messages are printed during module removal/reboot.
> 
> 'aead' (ffffffffa017c050): does not have a release() function, it is broken
> and must be fixed.
> 'bridge'
> 'cdrom'

<snip>

You will find that all of these are modules, right?  That's being worked
on still.

Again, please fix your code not to have an empty release function.  Will
you revert this change and fix it properly?

thanks,

greg k-h
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