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

[Tina Yang <tina.yang@xxxxxxxxxx>]

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@xxxxxxxxxx>
> > > Cc: Konrad Rzeszutek Wilk<konrad.wilk@xxxxxxxxxx>
> > > Cc: Jeremy Fitzhardinge<jeremy@xxxxxxxx>
> > > Signed-off-by: Zhenzhong.Duan<zhenzhong.duan@xxxxxxxxxx>
> > > Tested-by: gurudas.pai<gurudas.pai@xxxxxxxxxx>
> > > ---
> > >   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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