timer: Permit statically-declared work with deferrable timers

Currently, you have to just define a delayed_work uninitialised, and then
initialise it before first use.  That's a tad clumsy.  At risk of playing
mind-games with the compiler, fooling it into doing pointer arithmetic
with compile-time-constants, this lets clients properly initialise delayed
work with deferrable timers statically.

This patch was inspired by the issues which lead Artem Bityutskiy to
commit 8eab945c5616fc984 ("sunrpc: make the cache cleaner workqueue
deferrable").

Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com>
Acked-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index f11100f..88238c1 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -127,12 +127,20 @@
 	.timer = TIMER_INITIALIZER(NULL, 0, 0),			\
 	}
 
+#define __DEFERRED_WORK_INITIALIZER(n, f) {			\
+	.work = __WORK_INITIALIZER((n).work, (f)),		\
+	.timer = TIMER_DEFERRED_INITIALIZER(NULL, 0, 0),	\
+	}
+
 #define DECLARE_WORK(n, f)					\
 	struct work_struct n = __WORK_INITIALIZER(n, f)
 
 #define DECLARE_DELAYED_WORK(n, f)				\
 	struct delayed_work n = __DELAYED_WORK_INITIALIZER(n, f)
 
+#define DECLARE_DEFERRED_WORK(n, f)				\
+	struct delayed_work n = __DEFERRED_WORK_INITIALIZER(n, f)
+
 /*
  * initialize a work item's function pointer
  */