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    SubjectRe: [PATCH] add netconsole support for xen-netfront
    On 1/13/2012 3:06 AM, Ian Campbell wrote:
    > On Thu, 2012-01-12 at 14:17 +0000, Konrad Rzeszutek Wilk wrote:
    >> On Wed, Jan 11, 2012 at 04:52:36PM +0800, Zhenzhong Duan wrote:
    >>> add polling interface to xen-netfront device to support netconsole
    >>>
    >> Ian, any thoughts on the spinlock changes?
    > What are they for?
    When I did this patch back in 2008, both netconsole and netdump
    were supported. Spin_lock w/o irqsave and irqrestore would cause
    netdump hang due to the unexpected change of the irq status.
    Although netdump is now obsolete, I think it's always a good practice
    to preserve caller's irq status as we had a very bad experience
    chasing a similar problem caused by such a irq change in RDS
    in the not too long ago past.
    > At a guess they are a necessary consequence of the new calling context.
    > However not all the drivers I looked at which supported netpool were
    > using the irqsave variants in this context so I guess it must be some
    > secondary effect.
    >
    > Anyway, the upshot is that I think the changelog needs to explain the
    > rationale for the locking change.
    >
    > Ian.
    >
    >>> Signed-off-by: Tina.Yang<tina.yang@oracle.com>
    >>> Cc: Konrad Rzeszutek Wilk<konrad.wilk@oracle.com>
    >>> Cc: Jeremy Fitzhardinge<jeremy@goop.org>
    >>> Signed-off-by: Zhenzhong.Duan<zhenzhong.duan@oracle.com>
    >>> Tested-by: gurudas.pai<gurudas.pai@oracle.com>
    >>> ---
    >>> drivers/net/xen-netfront.c | 57 ++++++++++++++++++++++++++-----------------
    >>> 1 files changed, 34 insertions(+), 23 deletions(-)
    >>>
    >>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
    >>> index fa67905..db638b4 100644
    >>> --- a/drivers/net/xen-netfront.c
    >>> +++ b/drivers/net/xen-netfront.c
    >>> @@ -489,6 +489,7 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
    >>> int frags = skb_shinfo(skb)->nr_frags;
    >>> unsigned int offset = offset_in_page(data);
    >>> unsigned int len = skb_headlen(skb);
    >>> + unsigned long flags;
    >>>
    >>> frags += DIV_ROUND_UP(offset + len, PAGE_SIZE);
    >>> if (unlikely(frags> MAX_SKB_FRAGS + 1)) {
    >>> @@ -498,12 +499,12 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
    >>> goto drop;
    >>> }
    >>>
    >>> - spin_lock_irq(&np->tx_lock);
    >>> + spin_lock_irqsave(&np->tx_lock, flags);
    >>>
    >>> if (unlikely(!netif_carrier_ok(dev) ||
    >>> (frags> 1&& !xennet_can_sg(dev)) ||
    >>> netif_needs_gso(skb, netif_skb_features(skb)))) {
    >>> - spin_unlock_irq(&np->tx_lock);
    >>> + spin_unlock_irqrestore(&np->tx_lock, flags);
    >>> goto drop;
    >>> }
    >>>
    >>> @@ -574,7 +575,7 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
    >>> if (!netfront_tx_slot_available(np))
    >>> netif_stop_queue(dev);
    >>>
    >>> - spin_unlock_irq(&np->tx_lock);
    >>> + spin_unlock_irqrestore(&np->tx_lock, flags);
    >>>
    >>> return NETDEV_TX_OK;
    >>>
    >>> @@ -1228,6 +1229,33 @@ static int xennet_set_features(struct net_device *dev,
    >>> return 0;
    >>> }
    >>>
    >>> +static irqreturn_t xennet_interrupt(int irq, void *dev_id)
    >>> +{
    >>> + struct net_device *dev = dev_id;
    >>> + struct netfront_info *np = netdev_priv(dev);
    >>> + unsigned long flags;
    >>> +
    >>> + spin_lock_irqsave(&np->tx_lock, flags);
    >>> +
    >>> + if (likely(netif_carrier_ok(dev))) {
    >>> + xennet_tx_buf_gc(dev);
    >>> + /* Under tx_lock: protects access to rx shared-ring indexes. */
    >>> + if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx))
    >>> + napi_schedule(&np->napi);
    >>> + }
    >>> +
    >>> + spin_unlock_irqrestore(&np->tx_lock, flags);
    >>> +
    >>> + return IRQ_HANDLED;
    >>> +}
    >>> +
    >>> +#ifdef CONFIG_NET_POLL_CONTROLLER
    >>> +static void xennet_poll_controller(struct net_device *dev)
    >>> +{
    >>> + xennet_interrupt(0, dev);
    >>> +}
    >>> +#endif
    >>> +
    >>> static const struct net_device_ops xennet_netdev_ops = {
    >>> .ndo_open = xennet_open,
    >>> .ndo_uninit = xennet_uninit,
    >>> @@ -1239,6 +1267,9 @@ static const struct net_device_ops xennet_netdev_ops = {
    >>> .ndo_validate_addr = eth_validate_addr,
    >>> .ndo_fix_features = xennet_fix_features,
    >>> .ndo_set_features = xennet_set_features,
    >>> +#ifdef CONFIG_NET_POLL_CONTROLLER
    >>> + .ndo_poll_controller = xennet_poll_controller,
    >>> +#endif
    >>> };
    >>>
    >>> static struct net_device * __devinit xennet_create_dev(struct xenbus_device *dev)
    >>> @@ -1448,26 +1479,6 @@ static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
    >>> return 0;
    >>> }
    >>>
    >>> -static irqreturn_t xennet_interrupt(int irq, void *dev_id)
    >>> -{
    >>> - struct net_device *dev = dev_id;
    >>> - struct netfront_info *np = netdev_priv(dev);
    >>> - unsigned long flags;
    >>> -
    >>> - spin_lock_irqsave(&np->tx_lock, flags);
    >>> -
    >>> - if (likely(netif_carrier_ok(dev))) {
    >>> - xennet_tx_buf_gc(dev);
    >>> - /* Under tx_lock: protects access to rx shared-ring indexes. */
    >>> - if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx))
    >>> - napi_schedule(&np->napi);
    >>> - }
    >>> -
    >>> - spin_unlock_irqrestore(&np->tx_lock, flags);
    >>> -
    >>> - return IRQ_HANDLED;
    >>> -}
    >>> -
    >>> static int setup_netfront(struct xenbus_device *dev, struct netfront_info *info)
    >>> {
    >>> struct xen_netif_tx_sring *txs;
    >>> --
    >>> 1.7.3
    >



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