timekeeping: Provide timekeeping_restore_shadow()

Functions which operate on the real timekeeper, e.g. do_settimeofday(),
have error conditions. If they are hit a full timekeeping update is still
required because the already committed operations modified the timekeeper.

When switching these functions to operate on the shadow timekeeper then the
full update can be avoided in the error case, but the modified shadow
timekeeper has to be restored.

Provide a helper function for that.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20241009-devel-anna-maria-b4-timers-ptp-timekeeping-v2-15-554456a44a15@linutronix.de

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index c30b1870fc58d7a3ac6ca14ccf377f3d8ef1db06..ed0e328fedd0232eb74b02e35a39358dd6acee90 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -774,6 +774,15 @@ static inline void tk_update_ktime_data(struct timekeeper *tk)
        tk->tkr_raw.base = ns_to_ktime(tk->raw_sec * NSEC_PER_SEC);
 }
 
+/*
+ * Restore the shadow timekeeper from the real timekeeper.
+ */
+static void timekeeping_restore_shadow(struct tk_data *tkd)
+{
+       lockdep_assert_held(&tkd->lock);
+       memcpy(&tkd->shadow_timekeeper, &tkd->timekeeper, sizeof(tkd->timekeeper));
+}
+
 static void timekeeping_update(struct tk_data *tkd, struct timekeeper *tk, unsigned int action)
 {
        lockdep_assert_held(&tkd->lock);
@@ -801,7 +810,7 @@ static void timekeeping_update(struct tk_data *tkd, struct timekeeper *tk, unsig
         * timekeeper structure on the next update with stale data
         */
        if (action & TK_MIRROR)
-               memcpy(&tkd->shadow_timekeeper, tk, sizeof(*tk));
+               timekeeping_restore_shadow(tkd);
 }
 
 static void timekeeping_update_from_shadow(struct tk_data *tkd, unsigned int action)