Re: [PATCH v2 3/7] [PATCH 3/8] can: CAN Network device driver and Netlink interface

Andrew Morton
2009-05-13T06:33:28Z

On Tue, 12 May 2009 11:28:00 +0200 Wolfgang Grandegger <wg@grandegger.com> wrote:

> +int can_restart_now(struct net_device *dev)
> +{
> + struct can_priv *priv = netdev_priv(dev);
> + struct net_device_stats *stats = &dev->stats;
> + struct sk_buff *skb;
> + struct can_frame *cf;
> + int err;
> +
> + /* Synchronize with dev->hard_start_xmit() */
> + netif_tx_lock(dev);
> +
> + /* Ensure that no more messages can go out */
> + if (netif_carrier_ok(dev))
> + netif_carrier_off(dev);
> +
> + /* Ensure that no more messages can come in */
> + err = priv->do_set_mode(dev, CAN_MODE_STOP);
> + if (err)
> + return err;
> +
> + /* Now it's save to clean up */
> + del_timer_sync(&priv->restart_timer);

This is deadlockable.

It calls del_timer_sync() while holding netif_tx_lock(). But the timer
handler (can_restart_now()) also takes netif_tx_lock(). So if the
timer handler is presently running, it's sitting there spinning in
netif_tx_lock(). And del_timer_sync() is sitting there waiting for the
timer handler to complete.