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).
Thanks,
Rafael
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