Date: Wed, 23 Jul 2008 08:54:52 +0000
From: Jarek Poplawski <jarkao2@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: Larry.Finger@lwfinger.net, kaber@trash.net,
	torvalds@linux-foundation.org, akpm@linux-foundation.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-wireless@vger.kernel.org, peterz@infradead.org,
	mingo@redhat.com
Subject: Re: Kernel WARNING: at net/core/dev.c:1330
	__netif_schedule+0x2c/0x98()
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On Wed, Jul 23, 2008 at 12:59:21AM -0700, David Miller wrote:
> From: Jarek Poplawski <jarkao2@gmail.com>
> Date: Wed, 23 Jul 2008 06:20:36 +0000
> 
> > PS: if there is nothing new in lockdep the classical method would
> > be to change this static array:
> > 
> > static struct lock_class_key
> > netdev_xmit_lock_key[ARRAY_SIZE(netdev_lock_type)];
> > 
> > to
> > 
> > static struct lock_class_key
> > netdev_xmit_lock_key[ARRAY_SIZE(netdev_lock_type)][MAX_NUM_TX_QUEUES];
> > 
> > and set lockdep classes per queue as well. (If we are sure we don't
> > need lockdep subclasses anywhere this could be optimized by using
> > one lock_class_key per 8 queues and spin_lock_nested()).
> 
> Unfortunately MAX_NUM_TX_QUEUES is USHORT_MAX, so this isn't really
> a feasible approach.

Is it used by real devices already? Maybe for the beginning we could
start with something less?

> spin_lock_nested() isn't all that viable either, as the subclass
> limit is something like 8.

This method would need to do some additional counting: depending of
a queue number each 8 subsequent queues share (are set to) the same
class and their number mod 8 gives the subqueue number for
spin_lock_nested().

I'll try to find if there is something new around this in lockdep.
(lockdep people added to CC.)

Jarek P.