virtio_pci: document why we defer kfree

The reason we defer kfree until release function is because it's a
general rule for kobjects: kfree of the reference counter itself is only
legal in the release function.

Previous patch didn't make this clear, document this in code.

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

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
index 4beaee384906..a5486e65e04b 100644
--- a/drivers/virtio/virtio_pci_legacy.c
+++ b/drivers/virtio/virtio_pci_legacy.c
@@ -216,6 +216,9 @@ static void virtio_pci_release_dev(struct device *_d)
         struct virtio_device *vdev = dev_to_virtio(_d);
         struct virtio_pci_device *vp_dev = to_vp_device(vdev);
 
+        /* As struct device is a kobject, it's not safe to
+         * free the memory (including the reference counter itself)
+         * until it's release callback. */
         kfree(vp_dev);
 }