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

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Date:	Mon, 27 Oct 2008 01:45:23 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	"Zhao, Yu" <yu.zhao@...el.com>
Cc:	Yu Zhao <yu.zhao@...scape.net>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"greg@...ah.com" <greg@...ah.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...nel.org" <stable@...nel.org>,
	Rakib Mullick <rakib.mullick@...il.com>
Subject: Re: [PATCH] pci: Fixing drivers/pci/search.c compilation warning.

On Mon, Oct 27, 2008 at 03:34:14PM +0800, Zhao, Yu wrote:
> >Erm, no, the 'dev' cannot be destroyed because the caller has a refcount
> >on it.  The physical device backing it might have gone away.  The dev
> 
> Why does the caller have a reference count? I don't see we increase the 
> reference count after the 'dev' is returned by following in 
> pci_get_dev_by_id():
> 
>         dev = bus_find_device(&pci_bus_type, dev_start, (void *)id,
>                               match_pci_dev_by_id);
> 
> And this 'dev' becomes the 'from' in the next loop, but it may be 
> destroyed before the 'pci_dev_get(from)', isn't it?

Either you've gone back to talking about pci_find_device() [which, yes, is
vulnerable to race conditions, we know that, it's not interesting to talk
about it], or you're refusing to take it on faith that pci_get_dev_by_id()
returns a device with an increased refcount.  And if you don't believe
that is true, please follow the code in bus_find_device() to prove it.

-- 
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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