[PATCH] lockdep: fix seqlock_init()

seqlock_init() needs to use spin_lock_init() for dynamic locks, so that
lockdep is notified about the presence of a new lock.

(this is a fallout of the recent networking merge, which started using
the so-far unused seqlock_init() API.)

This fix solves the following lockdep-internal warning on current -git:

 INFO: trying to register non-static key.
 the code is fine but needs lockdep annotation.
 turning off the locking correctness validator.
     __lock_acquire+0x10c/0x9f9
     lock_acquire+0x56/0x72
     _spin_lock+0x35/0x42
     neigh_destroy+0x9d/0x12e
     neigh_periodic_timer+0x10a/0x15c
     run_timer_softirq+0x126/0x18e
     __do_softirq+0x6b/0xe6
     do_softirq+0x64/0xd2
     ksoftirqd+0x82/0x138
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

include/linux/seqlock.h

@@ -44,8 +44,11 @@ typedef struct {
 #define SEQLOCK_UNLOCKED \
 		 __SEQLOCK_UNLOCKED(old_style_seqlock_init)
 
-#define seqlock_init(x) \
-		do { *(x) = (seqlock_t) __SEQLOCK_UNLOCKED(x); } while (0)
+#define seqlock_init(x)					\
+	do {						\
+		(x)->sequence = 0;			\
+		spin_lock_init(&(x)->lock);		\
+	} while (0)
 
 #define DEFINE_SEQLOCK(x) \
 		seqlock_t x = __SEQLOCK_UNLOCKED(x)