From: Peter Hilber Date: Mon, 18 Dec 2023 07:38:41 +0000 (+0100) Subject: timekeeping: Fix cross-timestamp interpolation for non-x86 X-Git-Tag: v5.10.214~196 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=c6fd906c3c337d99ab08ee97a30b8983d82bab1d;p=thirdparty%2Fkernel%2Fstable.git timekeeping: Fix cross-timestamp interpolation for non-x86 [ Upstream commit 14274d0bd31b4debf28284604589f596ad2e99f2 ] So far, get_device_system_crosststamp() unconditionally passes system_counterval.cycles to timekeeping_cycles_to_ns(). But when interpolating system time (do_interp == true), system_counterval.cycles is before tkr_mono.cycle_last, contrary to the timekeeping_cycles_to_ns() expectations. On x86, CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE will mitigate on interpolating, setting delta to 0. With delta == 0, xtstamp->sys_monoraw and xtstamp->sys_realtime are then set to the last update time, as implicitly expected by adjust_historical_crosststamp(). On other architectures, the resulting nonsense xtstamp->sys_monoraw and xtstamp->sys_realtime corrupt the xtstamp (ts) adjustment in adjust_historical_crosststamp(). Fix this by deriving xtstamp->sys_monoraw and xtstamp->sys_realtime from the last update time when interpolating, by using the local variable "cycles". The local variable already has the right value when interpolating, unlike system_counterval.cycles. Fixes: 2c756feb18d9 ("time: Add history to cross timestamp interface supporting slower devices") Signed-off-by: Peter Hilber Signed-off-by: Thomas Gleixner Acked-by: John Stultz Link: https://lore.kernel.org/r/20231218073849.35294-4-peter.hilber@opensynergy.com Signed-off-by: Sasha Levin --- diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 6f615db414769..629a07e6a0bfc 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1248,10 +1248,8 @@ int get_device_system_crosststamp(int (*get_time_fn) tk_core.timekeeper.offs_real); base_raw = tk->tkr_raw.base; - nsec_real = timekeeping_cycles_to_ns(&tk->tkr_mono, - system_counterval.cycles); - nsec_raw = timekeeping_cycles_to_ns(&tk->tkr_raw, - system_counterval.cycles); + nsec_real = timekeeping_cycles_to_ns(&tk->tkr_mono, cycles); + nsec_raw = timekeeping_cycles_to_ns(&tk->tkr_raw, cycles); } while (read_seqcount_retry(&tk_core.seq, seq)); xtstamp->sys_realtime = ktime_add_ns(base_real, nsec_real);