linux-kernel - Re: [PATCH -v3 40/47] PCI: Add pci bus removal through /sys/.../pci

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Message-ID: <4F7F184A.3080001@gmail.com>
Date:	Sat, 07 Apr 2012 00:22:34 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Yinghai Lu <yhlu.kernel@...il.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>, x86 <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Randy Dunlap <rdunlap@...otime.net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH -v3 40/47] PCI: Add pci bus removal through /sys/.../pci_bus/.../remove

On 04/07/2012 12:07 AM, Bjorn Helgaas wrote:
> On Fri, Apr 6, 2012 at 10:01 AM, Yinghai Lu <yhlu.kernel@...il.com> wrote:
>> On Fri, Apr 6, 2012 at 8:50 AM, Jiang Liu <liuj97@...il.com> wrote:
>>> Hi Yinghai,
>>>        I found many other drivers assume that a pci bus won't disappear if
>>> the corresponding PCI bridge device still exists. The sysfs interface proposed
>>> here breaks that assumption and may cause many access-after-free issues.
>>> So what's the purpose of this interface? Should we remove this interface or
>>> enhance other drivers to avoid invalid memory access issues?
> 
> Can you point out some of the specifics about drivers making this
> assumption?  I'm not thrilled about the idea of removing a pci_bus
> while the upstream bridge pci_dev still exists either.
According to my understanding, following drivers may have such an assumption:
acpiphp, pciehp, shpcphp, acpi/pci_slot, acpi/pci_bind.
I suspect there are still other drivers have such issues.

> 
>> ok, will make it only show up on root bus.
> 
> OK.  I'm still interested in the specifics because I don't like the
> way the pci_bus is exposed, even inside the kernel.  The bus itself is
> not an active entity, and we can't really do anything with it except
> by touching a device connected to it.
> 
> Bjorn

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