Subject: [BPQ] lockdep: fix false positive

From: Ralf Baechle <[email-masked]>
Date: Mon, 10 Jul 2006 16:53:34 +0100

Bpqether is encapsulating AX.25 frames into ethernet frames.  There is a
virtual bpqether device paired with each ethernet devices, so it's normal
to pass through dev_queue_xmit twice for each frame which triggers the
locking detector.

Signed-off-by: Ralf Baechle <[email-masked]>

---
 drivers/net/hamradio/bpqether.c |    7 +++++++
 1 file changed, 7 insertions(+)

Index: linux-net/drivers/net/hamradio/bpqether.c
===================================================================
--- linux-net.orig/drivers/net/hamradio/bpqether.c	2006-07-09 02:47:59.000000000 +0100
+++ linux-net/drivers/net/hamradio/bpqether.c	2006-07-10 14:18:48.000000000 +0100
@@ -122,6 +122,12 @@ struct bpqdev {
 
 static LIST_HEAD(bpq_devices);
 
+/*
+ * bpqether network devices are paired with ethernet devices below them, so
+ * form a special "super class" of normal ethernet devices; split their locks
+ * off into a separate class since they always nest.
+ */
+static struct lock_class_key bpq_netdev_xmit_lock_key;
 
 /* ------------------------------------------------------------------------ */
 
@@ -528,6 +534,7 @@ static int bpq_new_device(struct net_dev
 	err = register_netdevice(ndev);
 	if (err)
 		goto error;
+	lockdep_set_class(&ndev->_xmit_lock, &bpq_netdev_xmit_lock_key);
 
 	/* List protected by RTNL */
 	list_add_rcu(&bpq->bpq_list, &bpq_devices);