workqueue: use irqsafe timer for delayed_work

Up to now, for delayed_works, try_to_grab_pending() couldn't be used
from IRQ handlers because IRQs may happen while
delayed_work_timer_fn() is in progress leading to indefinite -EAGAIN.

This patch makes delayed_work use the new TIMER_IRQSAFE flag for
delayed_work->timer.  This makes try_to_grab_pending() and thus
mod_delayed_work_on() safe to call from IRQ handlers.

Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index e84ebb6..d86b320 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -136,7 +136,8 @@
 #define __DELAYED_WORK_INITIALIZER(n, f, tflags) {			\
 	.work = __WORK_INITIALIZER((n).work, (f)),			\
 	.timer = __TIMER_INITIALIZER(delayed_work_timer_fn,		\
-			0, (unsigned long)&(n), (tflags)),		\
+				     0, (unsigned long)&(n),		\
+				     (tflags) | TIMER_IRQSAFE),		\
 	}
 
 #define DECLARE_WORK(n, f)						\
@@ -214,7 +215,8 @@
 	do {								\
 		INIT_WORK(&(_work)->work, (_func));			\
 		__setup_timer(&(_work)->timer, delayed_work_timer_fn,	\
-			      (unsigned long)(_work), (_tflags));	\
+			      (unsigned long)(_work),			\
+			      (_tflags) | TIMER_IRQSAFE);		\
 	} while (0)
 
 #define __INIT_DELAYED_WORK_ONSTACK(_work, _func, _tflags)		\
@@ -223,7 +225,7 @@
 		__setup_timer_on_stack(&(_work)->timer,			\
 				       delayed_work_timer_fn,		\
 				       (unsigned long)(_work),		\
-				       (_tflags));			\
+				       (_tflags) | TIMER_IRQSAFE);	\
 	} while (0)
 
 #define INIT_DELAYED_WORK(_work, _func)					\