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Re: [Xen-devel] [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@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk<konrad.wilk@xxxxxxxxxx>
Cc: Jeremy Fitzhardinge<jeremy@xxxxxxxx>
Signed-off-by: Zhenzhong.Duan<zhenzhong.duan@xxxxxxxxxx>
Tested-by: gurudas.pai<gurudas.pai@xxxxxxxxxx>
---
  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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