workqueue: set delayed_work->timer function on initialization

delayed_work->timer.function is currently initialized during
queue_delayed_work_on().  Export delayed_work_timer_fn() and set
delayed_work timer function during delayed_work initialization
together with other fields.

This ensures the timer function is always valid on an initialized
delayed_work.  This is to help mod_delayed_work() implementation.

To detect delayed_work users which diddle with the internal timer,
trigger WARN if timer function doesn't match on queue.
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/workqueue.h

@@ -16,6 +16,7 @@ struct workqueue_struct;
 
 struct work_struct;
 typedef void (*work_func_t)(struct work_struct *work);
+void delayed_work_timer_fn(unsigned long __data);
 
 /*
  * The first word is the work queue pointer and the flags rolled into
@@ -124,12 +125,14 @@ struct execute_work {
 
 #define __DELAYED_WORK_INITIALIZER(n, f) {			\
 	.work = __WORK_INITIALIZER((n).work, (f)),		\
-	.timer = TIMER_INITIALIZER(NULL, 0, 0),			\
+	.timer = TIMER_INITIALIZER(delayed_work_timer_fn,	\
+				0, (unsigned long)&(n)),	\
 	}
 
 #define __DEFERRED_WORK_INITIALIZER(n, f) {			\
 	.work = __WORK_INITIALIZER((n).work, (f)),		\
-	.timer = TIMER_DEFERRED_INITIALIZER(NULL, 0, 0),	\
+	.timer = TIMER_DEFERRED_INITIALIZER(delayed_work_timer_fn, \
+				0, (unsigned long)&(n)),	\
 	}
 
 #define DECLARE_WORK(n, f)					\
@@ -207,18 +210,24 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; }
 	do {							\
 		INIT_WORK(&(_work)->work, (_func));		\
 		init_timer(&(_work)->timer);			\
+		(_work)->timer.function = delayed_work_timer_fn;\
+		(_work)->timer.data = (unsigned long)(_work);	\
 	} while (0)
 
 #define INIT_DELAYED_WORK_ONSTACK(_work, _func)			\
 	do {							\
 		INIT_WORK_ONSTACK(&(_work)->work, (_func));	\
 		init_timer_on_stack(&(_work)->timer);		\
+		(_work)->timer.function = delayed_work_timer_fn;\
+		(_work)->timer.data = (unsigned long)(_work);	\
 	} while (0)
 
 #define INIT_DELAYED_WORK_DEFERRABLE(_work, _func)		\
 	do {							\
 		INIT_WORK(&(_work)->work, (_func));		\
 		init_timer_deferrable(&(_work)->timer);		\
+		(_work)->timer.function = delayed_work_timer_fn;\
+		(_work)->timer.data = (unsigned long)(_work);	\
 	} while (0)
 
 /**

kernel/workqueue.c

@@ -1112,7 +1112,7 @@ bool queue_work(struct workqueue_struct *wq, struct work_struct *work)
 }
 EXPORT_SYMBOL_GPL(queue_work);
 
-static void delayed_work_timer_fn(unsigned long __data)
+void delayed_work_timer_fn(unsigned long __data)
 {
 	struct delayed_work *dwork = (struct delayed_work *)__data;
 	struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);
@@ -1121,6 +1121,7 @@ static void delayed_work_timer_fn(unsigned long __data)
 	__queue_work(smp_processor_id(), cwq->wq, &dwork->work);
 	local_irq_enable();
 }
+EXPORT_SYMBOL_GPL(delayed_work_timer_fn);
 
 /**
  * queue_delayed_work_on - queue work on specific CPU after delay
@@ -1145,6 +1146,8 @@ bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 	if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
 		unsigned int lcpu;
 
+		WARN_ON_ONCE(timer->function != delayed_work_timer_fn ||
+			     timer->data != (unsigned long)dwork);
 		BUG_ON(timer_pending(timer));
 		BUG_ON(!list_empty(&work->entry));
 
@@ -1168,8 +1171,6 @@ bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 		set_work_cwq(work, get_cwq(lcpu, wq), 0);
 
 		timer->expires = jiffies + delay;
-		timer->data = (unsigned long)dwork;
-		timer->function = delayed_work_timer_fn;
 
 		if (unlikely(cpu >= 0))
 			add_timer_on(timer, cpu);