[PATCH] lockdep: annotate ieee1394 skb-queue-head locking

ieee1394 reuses the skb infrastructure of the networking code, and uses two
skb-head queues: ->pending_packet_queue and hpsbpkt_queue.  The latter is used
in the usual fashion: processed from a kernel thread.  The other one,
->pending_packet_queue is also processed from hardirq context (f.e.  in
hpsb_bus_reset()), which is not what the networking code usually does (which
completes from softirq or process context).  This locking assymetry can be
totally correct if done carefully, but it can also be dangerous if networking
helper functions are reused, which could assume traditional networking use.

It would probably be more robust to push this completion into a workqueue -
but technically the code can be 100% correct, and lockdep has to be taught
about it.  The solution is to split the ->pending_packet_queue skb-head->lock
class from the networking lock-class by using a private lock-validator key.

Has no effect on non-lockdep kernels.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>
Cc: Jody McIntyre <scjody@modernduck.com>
Cc: Ben Collins <bcollins@debian.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/ieee1394/hosts.c

@@ -107,6 +107,14 @@ static int alloc_hostnum_cb(struct hpsb_host *host, void *__data)
  */
 static DEFINE_MUTEX(host_num_alloc);
 
+/*
+ * The pending_packet_queue is special in that it's processed
+ * from hardirq context too (such as hpsb_bus_reset()). Hence
+ * split the lock class from the usual networking skb-head
+ * lock class by using a separate key for it:
+ */
+static struct lock_class_key pending_packet_queue_key;
+
 struct hpsb_host *hpsb_alloc_host(struct hpsb_host_driver *drv, size_t extra,
 				  struct device *dev)
 {
@@ -128,6 +136,8 @@ struct hpsb_host *hpsb_alloc_host(struct hpsb_host_driver *drv, size_t extra,
 	h->driver = drv;
 
 	skb_queue_head_init(&h->pending_packet_queue);
+	lockdep_set_class(&h->pending_packet_queue.lock,
+			   &pending_packet_queue_key);
 	INIT_LIST_HEAD(&h->addr_space);
 
 	for (i = 2; i < 16; i++)