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>

diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
index 4beaee3849069b414c4d9fcb1a7da89d62ca1083..a5486e65e04bd55d5c64a33d3dbeeadb27dd4857 100644 (file)
--- 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);
 }