virtio_pci: defer kfree until release callback

commit 63bd62a08ca45a0c804c3c89777edc7f76a2d6da upstream.

A struct device which has just been unregistered can live on past the
point at which a driver decides to drop it's initial reference to the
kobject gained on allocation.

This implies that when releasing a virtio device, we can't free a struct
virtio_device until the underlying struct device has been released,
which might not happen immediately on device_unregister().

Unfortunately, this is exactly what virtio pci does:
it has an empty release callback, and frees memory immediately
after unregistering the device.

This causes an easy to reproduce crash if CONFIG_DEBUG_KOBJECT_RELEASE
it enabled.

To fix, free the memory only once we know the device is gone in the release
callback.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 03d1984..65c907d 100644 (file)
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -612,11 +612,10 @@ static struct virtio_config_ops virtio_pci_config_ops = {
 
 static void virtio_pci_release_dev(struct device *_d)
 {
-       /*
-        * No need for a release method as we allocate/free
-        * all devices together with the pci devices.
-        * Provide an empty one to avoid getting a warning from core.
-        */
+       struct virtio_device *vdev = dev_to_virtio(_d);
+       struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+
+       kfree(vp_dev);
 }
 
 /* the PCI probing function */
@@ -704,7 +703,6 @@ static void __devexit virtio_pci_remove(struct pci_dev *pci_dev)
        pci_iounmap(pci_dev, vp_dev->ioaddr);
        pci_release_regions(pci_dev);
        pci_disable_device(pci_dev);
-       kfree(vp_dev);
 }
 
 #ifdef CONFIG_PM