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Message-ID: <4F15EB3E.3060700@oracle.com>
Date: Tue, 17 Jan 2012 13:42:22 -0800
From: Tina Yang <tina.yang@...cle.com>
To: Ian Campbell <Ian.Campbell@...rix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Zhenzhong Duan <zhenzhong.duan@...cle.com>,
"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"gurudas.pai@...cle.com" <gurudas.pai@...cle.com>,
Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [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@...cle.com>
>>> Cc: Konrad Rzeszutek Wilk<konrad.wilk@...cle.com>
>>> Cc: Jeremy Fitzhardinge<jeremy@...p.org>
>>> Signed-off-by: Zhenzhong.Duan<zhenzhong.duan@...cle.com>
>>> Tested-by: gurudas.pai<gurudas.pai@...cle.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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