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vfio: Protect vfio_dev_present against device_del

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vfio_dev_present is meant to give us a wait_event callback so that we
can block removing a device from vfio until it becomes unused.  The
root of this check depends on being able to get the iommu group from
the device.  Unfortunately if the BUS_NOTIFY_DEL_DEVICE notifier has
fired then the device-group reference is no longer searchable and we
fail the lookup.

We don't need to go to such extents for this though.  We have a
reference to the device, from which we can acquire a reference to the
group.  We can then use the group reference to search for the device
and properly block removal.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
This commit is contained in:
Alex Williamson 2013-02-14 14:02:13 -07:00
parent 906ee99dd2
commit e014e9444a
1 changed files with 12 additions and 21 deletions
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33
drivers/vfio/vfio.c
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@ -642,33 +642,16 @@ int vfio_add_group_dev(struct device *dev,
}
EXPORT_SYMBOL_GPL(vfio_add_group_dev);
/* Test whether a struct device is present in our tracking */
static bool vfio_dev_present(struct device *dev)
/* Given a referenced group, check if it contains the device */
static bool vfio_dev_present(struct vfio_group *group, struct device *dev)
{
struct iommu_group *iommu_group;
struct vfio_group *group;
struct vfio_device *device;
iommu_group = iommu_group_get(dev);
if (!iommu_group)
return false;
group = vfio_group_get_from_iommu(iommu_group);
if (!group) {
iommu_group_put(iommu_group);
return false;
}
device = vfio_group_get_device(group, dev);
if (!device) {
vfio_group_put(group);
iommu_group_put(iommu_group);
if (!device)
return false;
}
vfio_device_put(device);
vfio_group_put(group);
iommu_group_put(iommu_group);
return true;
}
@ -682,10 +665,18 @@ void *vfio_del_group_dev(struct device *dev)
struct iommu_group *iommu_group = group->iommu_group;
void *device_data = device->device_data;
/*
* The group exists so long as we have a device reference. Get
* a group reference and use it to scan for the device going away.
*/
vfio_group_get(group);
vfio_device_put(device);
/* TODO send a signal to encourage this to be released */
wait_event(vfio.release_q, !vfio_dev_present(dev));
wait_event(vfio.release_q, !vfio_dev_present(group, dev));
vfio_group_put(group);
iommu_group_put(iommu_group);