softirqs are invoked while bottom halves are masked

[David Miller]

From: Thomas De Schampheleire <patrickdepinguin+linuxppc at gmail.com>
Date: Tue, 12 Jul 2011 11:23:28 +0200

> Note that the reason we are seeing this problem, may be because the
> kernel we are using contains some patches from Freescale.
> Specifically, in dev_queue_xmit(), support is added for hardware queue
> handling, just before entering the rcu_read_lock_bh():
> 
>         if (dev->features & NETIF_F_HW_QDISC) {
>                 txq = dev_pick_tx(dev, skb);
>                 return dev_hard_start_xmit(skb, dev, txq);
>         }
> 
>         /* Disable soft irqs for various locks below. Also
>          * stops preemption for RCU.
>          */
>         rcu_read_lock_bh();
> 
> We just tried moving the escaping to dev_hard_start_xmit() after
> taking the lock, but this gives a large number of other problems, e.g.

This is definitely why you are seeing this behavior.

You cannot invoke dev_hard_start_xmit() without softirqs
being disabled.  It breaks everything.

This is what happens when you integrate networking patches
which were not reviewed and vetted on netdev.