Re: softirqs are invoked while bottom halves are masked

From: Thomas De Schampheleire <redacted>
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.