timekeeping: Update auxiliary timekeepers on clocksource change

Propagate a system clocksource change to the auxiliary timekeepers so that
they can pick up the new clocksource.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20250625183757.803890875@linutronix.de

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 7d3693a72a01120501e9061d5a110bd508d2f83c..ee9757018341f92ff7fc743de900ed107efbb023 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -119,8 +119,10 @@ static struct tk_fast tk_fast_raw  ____cacheline_aligned = {
 
 #ifdef CONFIG_POSIX_AUX_CLOCKS
 static __init void tk_aux_setup(void);
+static void tk_aux_update_clocksource(void);
 #else
 static inline void tk_aux_setup(void) { }
+static inline void tk_aux_update_clocksource(void) { }
 #endif
 
 unsigned long timekeeper_lock_irqsave(void)
@@ -1548,6 +1550,8 @@ static int change_clocksource(void *data)
                timekeeping_update_from_shadow(&tk_core, TK_UPDATE_ALL);
        }
 
+       tk_aux_update_clocksource();
+
        if (old) {
                if (old->disable)
                        old->disable(old);
@@ -2651,6 +2655,35 @@ EXPORT_SYMBOL(hardpps);
 #endif /* CONFIG_NTP_PPS */
 
 #ifdef CONFIG_POSIX_AUX_CLOCKS
+
+/*
+ * Bitmap for the activated auxiliary timekeepers to allow lockless quick
+ * checks in the hot paths without touching extra cache lines. If set, then
+ * the state of the corresponding timekeeper has to be re-checked under
+ * timekeeper::lock.
+ */
+static unsigned long aux_timekeepers;
+
+/* Invoked from timekeeping after a clocksource change */
+static void tk_aux_update_clocksource(void)
+{
+       unsigned long active = READ_ONCE(aux_timekeepers);
+       unsigned int id;
+
+       for_each_set_bit(id, &active, BITS_PER_LONG) {
+               struct tk_data *tkd = &timekeeper_data[id + TIMEKEEPER_AUX_FIRST];
+               struct timekeeper *tks = &tkd->shadow_timekeeper;
+
+               guard(raw_spinlock_irqsave)(&tkd->lock);
+               if (!tks->clock_valid)
+                       continue;
+
+               timekeeping_forward_now(tks);
+               tk_setup_internals(tks, tk_core.timekeeper.tkr_mono.clock);
+               timekeeping_update_from_shadow(tkd, TK_UPDATE_ALL);
+       }
+}
+
 static __init void tk_aux_setup(void)
 {
        for (int i = TIMEKEEPER_AUX_FIRST; i <= TIMEKEEPER_AUX_LAST; i++)