Messages in this thread | | | Date | Wed, 26 Sep 2007 15:10:51 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 3/3] UML - Correctly handle skb allocation failures |
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On Wed, 26 Sep 2007 17:46:13 -0400 Jeff Dike <jdike@addtoit.com> 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 <jdike@linux.intel.com> > --- > 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(); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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