Re: [PATCH] PCI: handle pci_sriov_set_totalvfs(dev, 0)

[Edward Cree <ecree@solarflare.com>]

On 01/08/14 04:18, Ethan Zhao wrote:
> On Thu, Jul 31, 2014 at 11:56 PM, Edward Cree <ecree@solarflare.com> wrote:
>> Clearing dev->is_physfn in the driver probe routine isn't safe:
>> dev->sriov memory can get leaked, for example, as sriov_init will get
>> called at device add, but sriov_release won't be called at removal.
>>
>   I think this memory leak bug doesn't exist.
>
>   The dev->sriov memory was allocated when pci_device_add() called.
> whenever devices
>   were hot-pluged into system or built-in devices were scanned while booting.
>
>   The memory of dev->sriov is to be freed by kobject->kobject_release() when
> the device reference counter reaches zero when put_device() was called.
> for hot-plug, that is pciehp_unconfigure_device()....etc.  but not in
> driver->remove().
>
Yes, but the problem is in pci_iov_release(), not how it gets called;
its code is
    if (dev->is_physfn)
        sriov_release(dev);
So if the device driver clears dev->is_physfn, and later on the device
is hot-unplugged, pci_iov_release() won't call sriov_release().
Thus any device driver that changes dev->is_physfn will, if the device
is hot-unplugged, leak dev->sriov.
Fortunately a quick grep shows no drivers doing this, so there's no
actual bug in existing code.  It's just that we can't use this approach
to disable SR-IOV from the driver's probe routine.
-Edward
>      put_device()
>         kobject_put()
>            kobject_release()
>                kobject_cleanup()
>                    device_release()
>                        dev->release(dev)
>                              pci_release_dev()
>                                   pci_release_capabilities()
>                                      pci_iov_release()
>                                          sriov_release(dev);
>                                                kfree(dev->sriov);
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