locking, sched: Give waitqueue spinlocks their own lockdep classes

Give waitqueue spinlocks their own lockdep classes when they
are initialised from init_waitqueue_head().  This means that
struct wait_queue::func functions can operate other waitqueues.

This is used by CacheFiles to catch the page from a backing fs
being unlocked and to wake up another thread to take a copy of
it.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Takashi Iwai <tiwai@suse.de>
Cc: linux-cachefs@redhat.com
Cc: torvalds@osdl.org
Cc: akpm@linux-foundation.org
LKML-Reference: <20090810113305.17284.81508.stgit@warthog.procyon.org.uk>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 2 deletions

diff --git a/kernel/wait.c b/kernel/wait.c
index ea7c3b4275cf..c4bd3d825f35 100644
--- a/kernel/wait.c
+++ b/kernel/wait.c
@@ -10,13 +10,14 @@
 #include <linux/wait.h>
 #include <linux/hash.h>
 
-void init_waitqueue_head(wait_queue_head_t *q)
+void __init_waitqueue_head(wait_queue_head_t *q, struct lock_class_key *key)
 {
         spin_lock_init(&q->lock);
+        lockdep_set_class(&q->lock, key);
         INIT_LIST_HEAD(&q->task_list);
 }
 
-EXPORT_SYMBOL(init_waitqueue_head);
+EXPORT_SYMBOL(__init_waitqueue_head);
 
 void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
 {