[PATCH 6.12 509/567] hrtimers: Introduce hrtimer_update_function()

Greg Kroah-Hartman
2026-01-06T17:42:23Z

From: Nam Cao <namcao@linutronix.de>

[ Upstream commit 8f02e3563bb5824eb01c94f2c75f1dcee2d05625 ]

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
Stable-dep-of: 267ee93c417e ("serial: xilinx_uartps: fix rs485 delay_rts_after_send")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/hrtimer.h | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -337,6 +337,28 @@ static inline int hrtimer_callback_runni
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);