On Wed, 26 Sep 2007 17:46:13 -0400
Jeff Dike <[email protected]> wrote:
> Handle memory allocation failures when reading packets.
>
> We have to read something from the host, even if we can't allocate any
> memory. If we don't, the host side of the device may fill up and stop
> delivering interrupts because no new packets can be queued.
>
> A single sk_buff is allocated whenever an MTU is seen which is larger
> than any seen earlier. This is used to read packets if there is a
> memory allocation failure.
>
> The large MTU check is done from eth_configure, which is called when a
> interface is added to the system, and from uml_net_change_mtu, which
> is called when an existing interface has its MTU changed.
>
> Signed-off-by: Jeff Dike <[email protected]>
> ---
> arch/um/drivers/net_kern.c | 60 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 60 insertions(+)
>
> Index: linux-2.6.20/arch/um/drivers/net_kern.c
> ===================================================================
> --- linux-2.6.20.orig/arch/um/drivers/net_kern.c 2007-09-26 16:48:21.000000000 -0400
> +++ linux-2.6.20/arch/um/drivers/net_kern.c 2007-09-26 16:56:16.000000000 -0400
> @@ -34,6 +34,48 @@ static inline void set_ether_mac(struct
> static DEFINE_SPINLOCK(opened_lock);
> static LIST_HEAD(opened);
>
> +/*
> + * The throwaway skb is used when we can't allocate an skb. The
> + * packet is read into throwaway in order to get the data off the
> + * connection to the host.
> + * It is reallocated whenever an MTU is seen which is larger than
> + * anything seen before. update_throwaway_skb is called from
> + * eth_configure for new interfaces and from uml_net_change_mtu for
> + * MTU changes on existing interfaces.
> + */
> +static DEFINE_SPINLOCK(throwaway_lock);
> +static struct sk_buff *throwaway;
> +static int throwaway_max;
> +
> +static int update_throwaway_skb(int max)
> +{
> + struct sk_buff *new;
> + int err = 0;
> +
> + spin_lock(&throwaway_lock);
> +
> + if (max <= throwaway_max)
> + goto out;
> +
> + err = -ENOMEM;
> + new = dev_alloc_skb(max);
> + if (new == NULL)
> + goto out;
> +
> + skb_put(new, max);
> +
> + kfree_skb(throwaway);
> + throwaway = new;
> + throwaway_max = max;
> + err = 0;
> +out:
> + spin_unlock(&throwaway_lock);
> +
> + return err;
> +}
> +
> +int npackets = 0;
Unneeded initialisation?
Maybe not a good name for a global symbol ;)
I worry that the memory at "throwaway" can get thrown away...
> static int uml_net_rx(struct net_device *dev)
> {
> struct uml_net_private *lp = dev->priv;
> @@ -42,7 +84,14 @@ static int uml_net_rx(struct net_device
>
> /* If we can't allocate memory, try again next round. */
> skb = dev_alloc_skb(lp->max_packet);
> + if ((++npackets % 100) == 0){
> + kfree_skb(skb);
> + skb = NULL;
> + }
> +
> if (skb == NULL) {
> + throwaway->dev = dev;
> + (*lp->read)(lp->fd, throwaway, lp);
... while other code is still using it. Are you sure we don't need
throwaway_lock here?
> lp->stats.rx_dropped++;
> return 0;
> }
> @@ -240,6 +289,13 @@ static int uml_net_set_mac(struct net_de
>
> static int uml_net_change_mtu(struct net_device *dev, int new_mtu)
> {
> + struct uml_net_private *lp = dev->priv;
> + int err;
> +
> + err = update_throwaway_skb(lp->max_packet);
> + if (err)
> + return err;
> +
> dev->mtu = new_mtu;
>
> return 0;
> @@ -447,6 +503,10 @@ static void eth_configure(int n, void *i
> dev->watchdog_timeo = (HZ >> 1);
> dev->irq = UM_ETH_IRQ;
>
> + err = update_throwaway_skb(lp->max_packet);
> + if (err)
> + goto out_undo_user_init;
> +
> rtnl_lock();
> err = register_netdevice(dev);
> rtnl_unlock();
-
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