Re: [patch] lockdep, annotate slocks: turn lockdep off for them

[Arjan van de Ven]

On Fri, 2006-06-30 at 15:45 -0700, Miles Lane wrote:
> Okay, I rebuilt my kernel with your combo patch applied.
> Then, I inserted my US Robotics USR2210 PCMCIA wifi card,
> ran "pccardutil eject", popped out the card and then inserted
> a Compaq iPaq wifi card.  This triggered the following.
> 
> [ INFO: possible circular locking dependency detected ]
> -------------------------------------------------------
> syslogd/1886 is trying to acquire lock:
>  (&dev->queue_lock){-+..}, at: [<c11a50b5>] dev_queue_xmit+0x120/0x24b
> 
> but task is already holding lock:
>  (&dev->_xmit_lock){-+..}, at: [<c11a5118>] dev_queue_xmit+0x183/0x24b
> 
> which lock already depends on the new lock.


ok this appears to be hostap playing games... it has 2 network devices
for one piece of hardware and one calls the other via the networking
layer; there is thankfully a natural ordering between the two, so just
making the slave one a separate type ought to make this work.

Can you test the patch below?

---
 drivers/net/wireless/hostap/hostap_hw.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

Index: linux-2.6.17-mm4/drivers/net/wireless/hostap/hostap_hw.c
===================================================================
--- linux-2.6.17-mm4.orig/drivers/net/wireless/hostap/hostap_hw.c
+++ linux-2.6.17-mm4/drivers/net/wireless/hostap/hostap_hw.c
@@ -3096,6 +3096,14 @@ static void prism2_clear_set_tim_queue(l
 }
 
 
+/*
+ * HostAP uses two layers of net devices, where the inner
+ * layer gets called all the time from the outer layer.
+ * This is a natural nesting, which needs a split lock type.
+ */
+static struct lock_class_key hostap_netdev_xmit_lock_key;
+
+
 static struct net_device *
 prism2_init_local_data(struct prism2_helper_functions *funcs, int card_idx,
 		       struct device *sdev)
@@ -3260,6 +3268,8 @@ while (0)
 	SET_NETDEV_DEV(dev, sdev);
 	if (ret >= 0)
 		ret = register_netdevice(dev);
+
+	lockdep_set_class(&dev->_xmit_lock, &hostap_netdev_xmit_lock_key);
 	rtnl_unlock();
 	if (ret < 0) {
 		printk(KERN_WARNING "%s: register netdevice failed!\n",


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