Re: [PATCH v2 04/10] PCI: Destroy pci dev only once

[Yinghai Lu]

[+ GregKH]

On Fri, Dec 6, 2013 at 5:27 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> On Thursday, December 05, 2013 10:52:36 PM Yinghai Lu wrote:
>> On Mon, Dec 2, 2013 at 6:49 AM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>> >
>> > Scenario 5: pci_stop_and_remove_bus_device() is run concurrently
>> >   for a device and its parent bridge via remove_callback().
>> >
>> >   In that case both code paths attempt to acquire
>> >   pci_remove_rescan_mutex.  If the child device removal acquires
>> >   it first, there will be no problems.  However, if the parent
>> >   bridge removal acquires it first, it will eventually execute
>> >   pci_destroy_dev() for the child device, but that device will
>> >   not be freed yet due to the reference held by the concurrent
>> >   child removal.  Consequently, both pci_stop_bus_device() and
>> >   pci_remove_bus_device() will be executed for that device
>> >   unnecessarily and pci_destroy_dev() will see a corrupted list
>> >   head in that object.  Moreover, an excess put_device() will
>> >   be executed for that device in that case which may lead to a
>> >   use-after-free in the final kobject_put() done by
>> >   sysfs_schedule_callback_work().
>> >
>> > Index: linux-pm/include/linux/pci.h
>> > ===================================================================
>> > --- linux-pm.orig/include/linux/pci.h
>> > +++ linux-pm/include/linux/pci.h
>> > @@ -321,6 +321,7 @@ struct pci_dev {
>> >         unsigned int    multifunction:1;/* Part of multi-function device */
>> >         /* keep track of device state */
>> >         unsigned int    is_added:1;
>> > +       unsigned int    is_gone:1;
>> >         unsigned int    is_busmaster:1; /* device is busmaster */
>> >         unsigned int    no_msi:1;       /* device may not use msi */
>> >         unsigned int    block_cfg_access:1;     /* config space access is blocked */
>> > Index: linux-pm/drivers/pci/remove.c
>> > ===================================================================
>> > --- linux-pm.orig/drivers/pci/remove.c
>> > +++ linux-pm/drivers/pci/remove.c
>> > @@ -34,6 +34,7 @@ static void pci_stop_dev(struct pci_dev
>> >
>> >  static void pci_destroy_dev(struct pci_dev *dev)
>> >  {
>> > +       dev->is_gone = 1;
>> >         device_del(&dev->dev);
>> >
>> >         down_write(&pci_bus_sem);
>> > @@ -109,8 +110,10 @@ static void pci_remove_bus_device(struct
>> >   */
>> >  void pci_stop_and_remove_bus_device(struct pci_dev *dev)
>> >  {
>> > -       pci_stop_bus_device(dev);
>> > -       pci_remove_bus_device(dev);
>> > +       if (!dev->is_gone) {
>> > +               pci_stop_bus_device(dev);
>> > +               pci_remove_bus_device(dev);
>> > +       }
>> >  }
>> >  EXPORT_SYMBOL(pci_stop_and_remove_bus_device);
>> >
>>
>> Yes, above change should address sys double remove problem.
>
> I've just realized that we don't need a new flag for that, though.
>
> It looks like we only need to check dev->dev.kobj.parent and return if that is
> NULL, because that means pci_destroy_dev() has run for that device already
> (I'm wondering why device_del() doesn't clear dev->parent, BTW, it looks like
> it should do that?).
>
> Of course, that still is going to be racy if we don't hold
> pci_remove_rescan_mutex around pci_stop_and_remove_bus_device() in every code
> path using it (or use another similar synchronization mechanism).

Wonder if we can have safe way to check if device_del() is called already.

And those access_after_free should be addressed by driver core instead
of pci code?

Thanks

Yinghai
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