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    SubjectRe: [PATCH v2 3/7] [PATCH 3/8] can: CAN Network device driver and Netlink interface
    Oliver Hartkopp wrote:
    > Andrew Morton wrote:
    >> 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.
    >>
    >>
    >>
    >
    > Hi Wolfgang,
    >
    > would it be an appropriate solution, just to invoke
    >
    > netif_stop_queue() in can_bus_off()
    >
    > and invoke
    >
    > netif_wake_queue() in can_restart_now()
    >
    > ???
    >
    > In a BUSOFF condition we're not able to send CAN frames anyway, so we
    > can disable the device queue and the we won't need any netif_tx_lock()
    > right?
    >
    > AFAIK this was the original implementation before some of the latest
    > improvement with the netif_carrier stuff.
    >
    > What do you think?

    The problem is the "manual" restart triggered via the netlink interface,
    which can occur in the middle of ndo_start_xmit().

    Wolfgang.



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