virtio_pci: defer kfree until release callback

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.

Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
index 08d19152702021407af7a67138c5850958f60a73..4beaee3849069b414c4d9fcb1a7da89d62ca1083 100644 (file)
--- a/drivers/virtio/virtio_pci_legacy.c
+++ b/drivers/virtio/virtio_pci_legacy.c
@@ -213,11 +213,10 @@ static const 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 */
@@ -311,5 +310,4 @@ void virtio_pci_legacy_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);
 }