Commit 63bd62a0 authored Jan 02, 2015 by Sasha Levin Committed by Michael S. Tsirkin Jan 06, 2015

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>

parent 945399a8

drivers/virtio/virtio_pci_legacy.c

+4 −6

Original line number	Diff line number	Diff line
		@@ -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);
		}