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    SubjectRe: [PATCH] pci: Fixing drivers/pci/search.c compilation warning.
    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

    dev = bus_find_device(&pci_bus_type, dev_start, (void *)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?

    > won't be destroyed until its reference count reaches zero, which could
    > be any time someone calls pci_dev_put() on it. In the scenario you're
    > postulating, it would happen in pci_get_dev_by_id():
    > if (from)
    > pci_dev_put(from);
    > which is the last time that 'from' is referred to in that callchain.

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      Last update: 2008-10-27 08:37    [W:0.040 / U:33.892 seconds]
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