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SubjectRe: [PATCH] add netconsole support for xen-netfront
On Wed, Jan 18, 2012 at 01:06:47PM -0800, Tina Yang wrote:
> On 1/18/2012 12:59 AM, Ian Campbell wrote:
> >On Tue, 2012-01-17 at 23:15 +0000, Tina Yang wrote:
> >>On 1/17/2012 1:51 PM, Konrad Rzeszutek Wilk wrote:
> >>>On Tue, Jan 17, 2012 at 01:42:22PM -0800, Tina Yang wrote:
> >>>>On 1/13/2012 3:06 AM, Ian Campbell wrote:
> >>>>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
> >>>Did you find the culprit of it? Was there a patch for that in the
> >>>upstream kernel?
> >>Yes. It has nothing to do with net drivers but same cause
> >>elsewhere in the kernel.
> >I didn't think start_xmit could be called with interrupts disabled or
> >from interrupt context but perhaps I am wrong about that or perhaps
> >netconsole changes things?
> Netdump does call it with interrupt disabled and hang because of
> it in 2.6.9 as I remember it. And you are right, netconsole has
> undergone changes from time to time, which also can change
> this specification.
> >
> >Right, Documentation/networking/netdevices.txt states that start_xmit
> >can be called with interrupts disabled by netconsole and therefore using
> >the irqsave/restore locking in this function is, AFAICT, correct.

Ok, so let me update the git commit description to include this.

I am listed as the maintainer but I would have thought that it should
go through David?

David, should it go through you or should I stick it in my tree? Here
is the patch with a better git description.

From 1c265b7946f222ab6a5aac5245a0ab84618772c8 Mon Sep 17 00:00:00 2001
From: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Date: Thu, 12 Jan 2012 10:18:29 +0800
Subject: [PATCH] xen/netfront: add netconsole support.

add polling interface to xen-netfront device to support netconsole

This patch also alters the spin_lock usage to use irqsave variant.
Documentation/networking/netdevices.txt states that start_xmit
can be called with interrupts disabled by netconsole and therefore using
the irqsave/restore locking in this function is looks correct.

Signed-off-by: Tina.Yang <tina.yang@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>
[v1: Copy-n-pasted Ian Campbell comments]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@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 d29365a..5a4b5df 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -478,6 +478,7 @@ 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)) {
@@ -487,12 +488,12 @@ 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;
}

@@ -561,7 +562,7 @@ 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;

@@ -1176,6 +1177,33 @@ static int xennet_set_features(struct net_device *dev, u32 features)
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,
@@ -1186,6 +1214,9 @@ 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)
@@ -1388,26 +1419,6 @@ 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;
--
1.7.7.5


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