linux-kernel - Re: [PATCH] pci: Fixing drivers/pci/search.c compilation warning.

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Date:	Sun, 26 Oct 2008 12:34:13 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Yu Zhao <yu.zhao@...scape.net>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>, linux-pci@...r.kernel.org,
	greg@...ah.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	Rakib Mullick <rakib.mullick@...il.com>
Subject: Re: [PATCH] pci: Fixing drivers/pci/search.c compilation warning.

On Sun, Oct 26, 2008 at 08:51:25PM +0800, Yu Zhao wrote:
> This reminds me of other problems of PCI search functions.
> 
> The 'dev_start' is passed to bus_find_device(), and its 'knode_bus' 
> reference count is decreased by klist_iter_init_node() in that function. 
> The problem is the reference count may be already decrease to 0 because 
> the PCI device 'from' is hot-plugged off (e.g., pci_remove_bus) when the 
> search goes. A warning is fired when klist_iter_init_node() detects the 
> reference count becomes 0.
> 
> Some code uses pci_find_device() in a way that is not safe with the 
> hotplug, because a device may be destroyed after bus_find_device() 
> returns it and before it's held by pci_dev_get() in the next round. 
> Following is an example from a random grep:

Yes, that's why pci_find_device() is deprecated.  But it doesn't also
need to be buggy ;-)

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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