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Message-ID: <20120117215100.GA25367@phenom.dumpdata.com>
Date: Tue, 17 Jan 2012 16:51:00 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Tina Yang <tina.yang@...cle.com>
Cc: Ian Campbell <Ian.Campbell@...rix.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 Tue, Jan 17, 2012 at 01:42:22PM -0800, Tina Yang wrote:
> 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.
Hm, that might have been due to the bug that was lurking in there since
2.6.27: d198d499148a0c64a41b3aba9e7dd43772832b91 "xen: x86_32: do not enable iterrupts when returning from exception in interrupt context"
> 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?
> in the not too long ago past.
OK, it sounds like it was issues in the past but might not be the
case anymore.
Could please re-test it without that spinlock irqsave patch using
the upstream kernel (or just UEK2 since it is an 3.0 type kernel).
Thanks.
> >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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