On Thu, Mar 24, 2016 at 09:56:21PM -0500, Bjorn Helgaas wrote:
> netpoll_setup() does a dev_hold() on np->dev, the netpoll device. If it
> fails, it correctly does a dev_put() but leaves np->dev set. If we call
> netpoll_cleanup() after the failure, np->dev is still set so we do another
> dev_put(), which decrements the refcount an extra time.
>
> It's questionable to call netpoll_cleanup() after netpoll_setup() fails,
> but it can be difficult to find the problem, and we can easily avoid it in
> this case. The extra decrements can lead to hangs like this:
>
> unregister_netdevice: waiting for bond0 to become free. Usage count = -3
>
> Set and clear np->dev at the points where we dev_hold() and dev_put() the
> device.
>
> Signed-off-by: Bjorn Helgaas <bhelg...@google.com>
> ---
> net/core/netpoll.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/netpoll.c b/net/core/netpoll.c
> index 94acfc8..a57bd17 100644
> --- a/net/core/netpoll.c
> +++ b/net/core/netpoll.c
> @@ -603,7 +603,6 @@ int __netpoll_setup(struct netpoll *np, struct net_device
> *ndev)
> const struct net_device_ops *ops;
> int err;
>
> - np->dev = ndev;
> strlcpy(np->dev_name, ndev->name, IFNAMSIZ);
> INIT_WORK(&np->cleanup_work, netpoll_async_cleanup);
>
> @@ -670,6 +669,7 @@ int netpoll_setup(struct netpoll *np)
> goto unlock;
> }
> dev_hold(ndev);
> + np->dev = ndev;
>
> if (netdev_master_upper_dev_get(ndev)) {
> np_err(np, "%s is a slave device, aborting\n", np->dev_name);
> @@ -770,6 +770,7 @@ int netpoll_setup(struct netpoll *np)
> return 0;
>
> put:
> + np->dev = NULL;
> dev_put(ndev);
> unlock:
> rtnl_unlock();
>
Is this safe for stacked devices? It makes good sense for the typical case, but
if you attempt to setup a netpoll client on a bridge/bond/vlan, etc, the lower
device will get its own netpoll struct registered and have no associated np->dev
pointer. It not be a real problem in practice, But you probably want to check
to make sure that stacked devices which recursively call the netpoll api don't
do anyting with the np->dev pointer.
Regards
Neil
