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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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