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SubjectRe: [PATCH] pci: Fixing drivers/pci/search.c compilation warning.
Zhao, Yu wrote:
> Matthew Wilcox wrote:
>> On Mon, Oct 27, 2008 at 03:13:51PM +0800, Zhao, Yu wrote:
>>> Matthew Wilcox wrote:
>>>> On Mon, Oct 27, 2008 at 11:18:43AM +0800, Zhao, Yu wrote:
>>>>> Matthew Wilcox wrote:
>>>>>> Yes, that's why pci_find_device() is deprecated. But it doesn't also
>>>>>> need to be buggy ;-)
>>>>> How about pci_get_bus_and_slot()? People would meet the problem with it
>>>>> anyway.
>>>> What problem with it? It's documented to return the device with an
>>>> increased refcount, and the implementation appears to do exactly that:
>>>>
>>> The 'dev' returned by pci_get_device() may be destroyed by PCI hotplug.
>>> I suppose that passing this 'dev' to pci_get_device() in the next loop
>>> would crash the system, right?
>> 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?

I checked the source code, there is no 'pci_dev_get(from)', the
reference count is increased in bus_find_device().

while ((dev = next_device(&i)))
if (match(dev, data) && get_device(dev))

But the essential problem is same: the reference count of 'dev' above
may be decreased before the 'get_device(dev)', I guess.


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