linux-kernel - Re: [PATCH] x86: mcheck: call put_device on device

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Message-ID: <20131203022330.GA25136@gchen.bj.intel.com>
Date:	Mon, 2 Dec 2013 21:23:30 -0500
From:	"Chen, Gong" <gong.chen@...ux.intel.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Levente Kurusa <levex@...ux.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Luck <tony.luck@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	EDAC <linux-edac@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: mcheck: call put_device on device_register failure

On Sat, Nov 30, 2013 at 12:12:14PM +0100, Borislav Petkov wrote:
> Date:	Sat, 30 Nov 2013 12:12:14 +0100
> From: Borislav Petkov <bp@...en8.de>
> To: Levente Kurusa <levex@...ux.com>
> Cc: Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
>  Tony Luck <tony.luck@...el.com>, "H. Peter Anvin" <hpa@...or.com>,
>  x86@...nel.org, EDAC <linux-edac@...r.kernel.org>, LKML
>  <linux-kernel@...r.kernel.org>
> Subject: Re: [PATCH] x86: mcheck: call put_device on device_register failure
> User-Agent: Mutt/1.5.21 (2010-09-15)
> 
> On Sat, Nov 30, 2013 at 08:30:33AM +0100, Levente Kurusa wrote:
> > No, if the call to put_device gives up the last reference to the
> > device, then device_release gets called which in turn frees the memory
> > associated with it. In this case, mce_device_release() will get
> > called, which is just a simple kfree call.
> 
> Aah, that's that delayed freeing the driver core does, right. Now you
> made me go and look into detail:
> 
> device_unregister
> |->put_device
>   |->kobject_put
>      |->kref_put(&kobj->kref, kobject_release)
> 	|->kref_sub(kref, 1, release)
> 	   |->release
> 	   |->kobject_release
> 	      |->kobject_cleanup
> 	         |->t->release
> 		 |->device_release
> 		    |->mce_device_release
> 
> 
> Ok, I see it now. :-) :-)
> 
> Thanks, I'll take your patch as-is.
> 

I have some concerns about it. if device_register is failed, it will
backtraces all kinds of conditions automatically, including put_device
definately. So do we really need an extra put_device when it returns
failure?

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