Subject: Re: [PATCH] add netconsole support for xen-netfront

From: Tina Yang <[email-masked]>
Date: Tue, 17 Jan 2012 13:42:22 -0800

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<[email-masked]>
>>> Cc: Konrad Rzeszutek Wilk<[email-masked]>
>>> Cc: Jeremy Fitzhardinge<[email-masked]>
>>> Signed-off-by: Zhenzhong.Duan<[email-masked]>
>>> Tested-by: gurudas.pai<[email-masked]>
>>> ---
>>>   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
>