From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [NET]: Add netif_tx_lock
Date: Mon, 05 Jun 2006 21:57:48 -0700 (PDT)
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From: Roland Dreier <rdreier@cisco.com>
Date: Mon, 05 Jun 2006 21:44:01 -0700

>  > IPOIB is going to BUG() with this change.  Because now, in their
>  > multicast code, you're going to local_bh_disable() via
>  > netif_tx_unlock() with hw IRQs disabled which is illegal.
>  > 
>  > It shows a bug here in the locking of the IPOIB driver.
> 
> Sorry, I haven't followed this thread closely.  Can you expand on what
> the bug in ipoib's multicast locking is?

It disables hw interrupts, and takes the xmit_lock.

xmit_lock is a BH only spinlock, you can't take it from hw
interrupts, or inside of a HW irq protected spinlock.

You can take it on the outside of a HW irq lock protected
area like this:

	spin_lock_bh(&dev->xmit_lock);

	spin_lock_irq(&whatever_lock);

	spin_unlock_irq(&whatever_lock);

	spin_unlock_bh(&dev->xmit_lock);

but not the other way around.