hrtimers: Introduce hrtimer_update_function()

Some users of hrtimer need to change the callback function after the
initial setup. They write to hrtimer::function directly.

That's not safe under all circumstances as the write is lockless and a
concurrent timer expiry might end up using the wrong function pointer.

Introduce hrtimer_update_function(), which also performs runtime checks
whether it is safe to modify the callback.

This allows to make hrtimer::function private once all users are converted.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20a937b0ae09ad54b5b6d86eabead7c570f1b72e.1730386209.git.namcao@linutronix.de

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 48872a2b40718cc7d0c1893651767a3c992483b9..6e026730e80392d9640e8de6fd1a2490f5640581 100644 (file)
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -327,6 +327,28 @@ static inline int hrtimer_callback_running(struct hrtimer *timer)
        return timer->base->running == timer;
 }
 
+/**
+ * hrtimer_update_function - Update the timer's callback function
+ * @timer:     Timer to update
+ * @function:  New callback function
+ *
+ * Only safe to call if the timer is not enqueued. Can be called in the callback function if the
+ * timer is not enqueued at the same time (see the comments above HRTIMER_STATE_ENQUEUED).
+ */
+static inline void hrtimer_update_function(struct hrtimer *timer,
+                                          enum hrtimer_restart (*function)(struct hrtimer *))
+{
+       guard(raw_spinlock_irqsave)(&timer->base->cpu_base->lock);
+
+       if (WARN_ON_ONCE(hrtimer_is_queued(timer)))
+               return;
+
+       if (WARN_ON_ONCE(!function))
+               return;
+
+       timer->function = function;
+}
+
 /* Forward a hrtimer so it expires after now: */
 extern u64
 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval);