timekeeping: Rework timekeeping_suspend() to use shadow_timekeeper

Updates of the timekeeper can be done by operating on the shadow timekeeper
and afterwards copying the result into the real timekeeper. This has the
advantage, that the sequence count write protected region is kept as small
as possible.

While the sequence count held time is not relevant for the resume path as
there is no concurrency, there is no reason to have this function
different than all the other update sites.

Convert timekeeping_inject_offset() to use this scheme and cleanup the
variable declarations while at it.

As halt_fast_timekeeper() does not need protection sequence counter, it is
no problem to move it with this change outside of the sequence counter
protected area. But it still needs to be executed while holding the lock.

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-v2-22-554456a44a15@linutronix.de

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 94f68e7ffc9df2ba86e326ecdff6e7eb94e09096..231eaa43a94a6bbe0172cc569d22566136aafcf5 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2003,11 +2003,11 @@ void timekeeping_resume(void)
 
 int timekeeping_suspend(void)
 {
-       struct timekeeper *tk = &tk_core.timekeeper;
-       unsigned long flags;
-       struct timespec64               delta, delta_delta;
-       static struct timespec64        old_delta;
+       struct timekeeper *tks = &tk_core.shadow_timekeeper;
+       struct timespec64 delta, delta_delta;
+       static struct timespec64 old_delta;
        struct clocksource *curr_clock;
+       unsigned long flags;
        u64 cycle_now;
 
        read_persistent_clock64(&timekeeping_suspend_time);
@@ -2023,8 +2023,7 @@ int timekeeping_suspend(void)
        suspend_timing_needed = true;
 
        raw_spin_lock_irqsave(&tk_core.lock, flags);
-       write_seqcount_begin(&tk_core.seq);
-       timekeeping_forward_now(tk);
+       timekeeping_forward_now(tks);
        timekeeping_suspended = 1;
 
        /*
@@ -2032,8 +2031,8 @@ int timekeeping_suspend(void)
         * just read from the current clocksource. Save this to potentially
         * use in suspend timing.
         */
-       curr_clock = tk->tkr_mono.clock;
-       cycle_now = tk->tkr_mono.cycle_last;
+       curr_clock = tks->tkr_mono.clock;
+       cycle_now = tks->tkr_mono.cycle_last;
        clocksource_start_suspend_timing(curr_clock, cycle_now);
 
        if (persistent_clock_exists) {
@@ -2043,7 +2042,7 @@ int timekeeping_suspend(void)
                 * try to compensate so the difference in system time
                 * and persistent_clock time stays close to constant.
                 */
-               delta = timespec64_sub(tk_xtime(tk), timekeeping_suspend_time);
+               delta = timespec64_sub(tk_xtime(tks), timekeeping_suspend_time);
                delta_delta = timespec64_sub(delta, old_delta);
                if (abs(delta_delta.tv_sec) >= 2) {
                        /*
@@ -2058,9 +2057,8 @@ int timekeeping_suspend(void)
                }
        }
 
-       timekeeping_update(&tk_core, tk, TK_MIRROR);
-       halt_fast_timekeeper(tk);
-       write_seqcount_end(&tk_core.seq);
+       timekeeping_update_from_shadow(&tk_core, 0);
+       halt_fast_timekeeper(tks);
        raw_spin_unlock_irqrestore(&tk_core.lock, flags);
 
        tick_suspend();