linux-kernel - Re: [PATCH] mce: fix warning messages about static struct mce

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Date:	Thu, 19 Jan 2012 13:32:23 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"Luck, Tony" <tony.luck@...el.com>, Greg KH <gregkh@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Sergei Trofimovich <slyich@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux PM mailing list <linux-pm@...r.kernel.org>,
	Borislav Petkov <bp@...64.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"prasad@...ux.vnet.ibm.com" <prasad@...ux.vnet.ibm.com>,
	Ming Lei <tom.leiming@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Borislav Petkov <borislav.petkov@....com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Andi Kleen <ak@...ux.intel.com>,
	"gouders@...bocholt.fh-gelsenkirchen.de" 
	<gouders@...bocholt.fh-gelsenkirchen.de>,
	Marcos Souza <marcos.mage@...il.com>,
	"justinmattock@...il.com" <justinmattock@...il.com>,
	Jeff Chua <jeff.chua.linux@...il.com>
Subject: Re: [PATCH] mce: fix warning messages about static struct mce_device


* Kay Sievers <kay.sievers@...y.org> wrote:

> > There's nothing special about the driver model code in this 
> > respect. The same restriction applies wherever object 
> > lifetimes are controlled by reference counting.
> 
> Right. But it might not be obvious what 's the background 
> here:
> 
> An allocated device object(memory) usually represents an 
> actual device(hardware). The object can have N users. Every of 
> the users is required to take a reference to the object, which 
> pins the object's memory as long as any of the N users might 
> need to access it.
> 
> In a hotplug world, we deal with device-removal.  On 
> disconnect, we usually just orphan the object, we remove it 
> from visibility, disconnect the device <-> object relation.
> 
> All of the N users with a reference can still access the 
> memory, they just do not talk to a real device anymore. The 
> invalidated/orphaned state is communicated otherwise by locks 
> and flags in the device object. Only after all of the N users 
> left the object alone, the memory of the orphan if free'd.

But this is not what happened here - it's a special piece of 
fundamental hardware that doesnt hot-plug separately from the 
CPU and that has just a single "user".

So i'm curious, why wasn't the memset() enough? It should have 
resolved the bug AFAICS.

Thanks,

	Ingo
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