"Michael S. Tsirkin" <mst@xxxxxxxxxx> writes:
> On device hot-unplug, 9p/virtio currently will kfree channel while
> it might still be in use.
>
> Of course, it might stay used forever, so it's an extremely ugly hack,
> but it seems better than use-after-free that we have now.
>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
I'll apply it, but it looks like a bandaid.
The right answer would seem to be:
1) Use reference counting: 1 for client, 1 for transport.
2) When hot unplug, complete (ie. fail) all outstanding requests.
3) From then on, fail all incoming requests.
4) When refcount hits 0, free the structure.
Thanks,
Rusty.
> ---
> net/9p/trans_virtio.c | 25 +++++++++++++++++++++----
> 1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index d8e376a..d1b2f306 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -658,14 +658,31 @@ p9_virtio_create(struct p9_client *client, const char *devname, char *args)
> static void p9_virtio_remove(struct virtio_device *vdev)
> {
> struct virtio_chan *chan = vdev->priv;
> -
> - if (chan->inuse)
> - p9_virtio_close(chan->client);
> - vdev->config->del_vqs(vdev);
> + unsigned long warning_time;
> + bool inuse;
>
> mutex_lock(&virtio_9p_lock);
> +
> + /* Remove self from list so we don't get new users. */
> list_del(&chan->chan_list);
> + warning_time = jiffies;
> +
> + /* Wait for existing users to close. */
> + while (chan->inuse) {
> + mutex_unlock(&virtio_9p_lock);
> + msleep(250);
> + if (time_after(jiffies, warning_time + 10 * HZ)) {
> + dev_emerg(&vdev->dev, "p9_virtio_remove: "
> + "waiting for device in use.\n");
> + warning_time = jiffies;
> + }
> + mutex_lock(&virtio_9p_lock);
> + }
> +
> mutex_unlock(&virtio_9p_lock);
> +
> + vdev->config->del_vqs(vdev);
> +
> sysfs_remove_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
> kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
> kfree(chan->tag);
> --
> MST
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