linux-kernel - Re: [PATCH 2.6.26] PCI: refuse to re-add a device to a bus upon pci_scan_child

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Date:	Tue, 22 Jul 2008 20:41:00 +0300
From:	Eran Liberty <liberty@...ricom.com>
To:	Matthew Wilcox <matthew@....cx>
CC:	eran liberty <eran.liberty@...il.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH 2.6.26] PCI: refuse to re-add a device to a bus upon pci_scan_child_bus()

Matthew Wilcox wrote:
> On Tue, Jul 22, 2008 at 06:25:40PM +0300, Eran Liberty wrote:
>   
>> If my devices where the only one on the bus I would not have stumbled on 
>> this bug. I would have removed them all before reloading and would have 
>> scanned and empty PCI bus list after the reloading.
>>     
>
> That's not true, the code you posted:
>
> bus = null;
> while ((bus = pci_find_next_bus(bus)) != NULL) {
>         pci_scan_child_bus(bus);
>         pci_bus_assign_resources(bus);
>         pci_bus_add_devices(bus);
> }
>
> will scan all busses again.
>   
You are correct! I have a single bus :)

>   
>> Alas, the CPU itself is a pci device. Upon scanning the bus it is it who 
>> is duplicated. Upon trying to "pci_bus_add_devices()" you get resource 
>> collision.
>>     
>
> Does the CPU have BARs of its own?  If you have no other devices with
> BARs, it would explain why you have not noticed the problem with
> fixup_resource ;-)
>   
I seriously doubt my CPU has any resources of its own.

>   
>> Do you perceive any down side to my suggested patch?
>> It seems (to me) really logical that a device can not and should not be 
>> added twice to a pci bus device list.
>>     
>
> The problem is the other side-effects of what you propose.
>   
Could you elaborate what ominous side-effects you predict?

Liberty
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