linux-kernel - Re: 2.6.24-rc4-mm1 kobject changes broken with hvcs driver on powerpc

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Message-ID: <20071206203118.GA28618@kroah.com>
Date:	Thu, 6 Dec 2007 12:31:18 -0800
From:	Greg KH <greg@...ah.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, rsa@...ibm.com, apw@...dowen.org,
	balbir@...ibm.com
Subject: Re: 2.6.24-rc4-mm1 kobject changes broken with hvcs driver on
	powerpc

On Fri, Dec 07, 2007 at 12:28:58AM +0530, Balbir Singh wrote:
> Greg KH wrote:
> 
> >> Why release the spinlock here? It's done after the count is incremented.
> >> This patch does not seem correct.
> > 
> > Doh, you are correct, I'll make sure that I fix this up before applying
> > it.
> > 
> > thanks,
> > 
> > greg k-h
> 
> Hi, Greg,
> 
> I ran some tests with the fixed up version of this patch and the system
> fails to come up.
> 
> I see the WARN_ON in lib/kref.c:33 and the system fails to boot beyond
> that point. I have not yet found time to debug it though.

That's not good, that warning means that someone has tried to use this
kref _before_ it was initialized, so there is a logic error in the code
that was previously being papered over with the lack of this message in
the kobject code.

I do have this same message availble as a patch for the kobject core, it
would be interesting if you could just run 2.6.24-rc4 with just this
patch:
	http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/gregkh-01-driver/kobject-warn.patch

it might take some fuzz to fit properly, but all you really want to do
is add:
	WARN_ON(atomic_read(&kobj->kref.refcount));
before the kref_init() call in kobject_init().

thanks,

greg k-h
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