To initialize hrtimer on stack, hrtimer_init_on_stack() needs to be called
and also hrtimer::function must be set. This is error-prone and awkward to
use.

Introduce hrtimer_setup_on_stack() which does both of these things, so that
users of hrtimer can be simplified.

The new setup function also has a sanity check for the provided function
pointer. If NULL, a warning is emitted and a dummy callback installed.

hrtimer_init_on_stack() will be removed as soon as all of its users have
been converted to the new function.

Signed-off-by: Nam Cao <namcao@linutronix.de>
---
 include/linux/hrtimer.h |  3 +++
 kernel/time/hrtimer.c   | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index bcc0715c59a8..2da513f8d66a 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -232,6 +232,9 @@ extern void hrtimer_setup(struct hrtimer *timer, enum hrtimer_restart (*function
 			  clockid_t clock_id, enum hrtimer_mode mode);
 extern void hrtimer_init_on_stack(struct hrtimer *timer, clockid_t which_clock,
 				  enum hrtimer_mode mode);
+extern void hrtimer_setup_on_stack(struct hrtimer *timer,
+				   enum hrtimer_restart (*function)(struct hrtimer *),
+				   clockid_t clock_id, enum hrtimer_mode mode);
 extern void hrtimer_init_sleeper_on_stack(struct hrtimer_sleeper *sl,
 					  clockid_t clock_id,
 					  enum hrtimer_mode mode);
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index a5ef67edcda9..daee4e27f839 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1646,6 +1646,25 @@ void hrtimer_init_on_stack(struct hrtimer *timer, clockid_t clock_id,
 }
 EXPORT_SYMBOL_GPL(hrtimer_init_on_stack);
 
+/**
+ * hrtimer_setup_on_stack - initialize a timer on stack memory
+ * @timer:	The timer to be initialized
+ * @function:	the callback function
+ * @clock_id:	The clock to be used
+ * @mode:       The timer mode
+ *
+ * Similar to hrtimer_setup(), except that this one must be used if struct hrtimer is in stack
+ * memory.
+ */
+void hrtimer_setup_on_stack(struct hrtimer *timer,
+			    enum hrtimer_restart (*function)(struct hrtimer *),
+			    clockid_t clock_id, enum hrtimer_mode mode)
+{
+	debug_init_on_stack(timer, clock_id, mode);
+	__hrtimer_setup(timer, function, clock_id, mode);
+}
+EXPORT_SYMBOL_GPL(hrtimer_setup_on_stack);
+
 /*
  * A timer is active, when it is enqueued into the rbtree or the
  * callback function is running or it's in the state of being migrated
-- 
2.39.5