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| author |   cheloha <cheloha@openbsd.org> | 2019-12-02 02:24:29 +0000 |
|---|---|---|
| committer | cheloha <cheloha@openbsd.org> | 2019-12-02 02:24:29 +0000 |
| commit | 1c733b92bb4dc807333a5780ab36f50df04fe341 (patch) | |
| tree | 8fb59259eab21242d0e478aea72222024c53f54f /sys/kern/kern_tc.c | |
| parent | output_createtmp() remembers the true name, so output_finish() does not (diff) | |
| download | wireguard-openbsd-1c733b92bb4dc807333a5780ab36f50df04fe341.tar.xz wireguard-openbsd-1c733b92bb4dc807333a5780ab36f50df04fe341.zip | |
tc_windup: separate timecounter.tc_freq_adj from timehands.th_adjustment
We currently mix timecounter.tc_freq_adj and timehands.th_adjtimedelta
in ntp_update_second() to produce timehands.th_adjustment, our net skew.
But if you set a low enough adjfreq(2) adjustment you can freeze time.
This prevents ntp_update_second() from running again. So even if you
then set a sane adjfreq(2) you cannot unfreeze time without rebooting.
If we just reread timecounter.tc_freq_adj every time we recompute
timehands.th_scale we avoid this trap. visa@ notes that this is
more costly than what we currently do but that the cost itself is
negligible.
Intuitively, timecounter.tc_freq_adj is a constant skew and should be
handled separately from timehands.th_adjtimedelta, an adjustment that
we chip away at very slowly.
tedu@ notes that this problem is sort-of an argument for imposing range
limits on adjfreq(2) inputs. He's right, but I think we should still
separate the counter adjustment from the adjtime(2) adjustment, with
or without range limits.
ok visa@
Diffstat (limited to 'sys/kern/kern_tc.c')
| -rw-r--r-- | sys/kern/kern_tc.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c index 2804e2ffbda..a911acc8f59 100644 --- a/sys/kern/kern_tc.c +++ b/sys/kern/kern_tc.c @@ -1,4 +1,4 @@ -/* $OpenBSD: kern_tc.c,v 1.51 2019/11/26 15:27:08 cheloha Exp $ */ +/* $OpenBSD: kern_tc.c,v 1.52 2019/12/02 02:24:29 cheloha Exp $ */ /* * Copyright (c) 2000 Poul-Henning Kamp <phk@FreeBSD.org> @@ -477,6 +477,7 @@ tc_windup(struct bintime *new_boottime, struct bintime *new_offset, struct bintime bt; struct timecounter *active_tc; struct timehands *th, *tho; + int64_t counter_adjustment; u_int64_t scale; u_int delta, ncount, ogen; int i; @@ -594,7 +595,8 @@ tc_windup(struct bintime *new_boottime, struct bintime *new_offset, * */ scale = (u_int64_t)1 << 63; - scale += (th->th_adjustment / 1024) * 2199; + counter_adjustment = th->th_counter->tc_freq_adj; + scale += ((th->th_adjustment + counter_adjustment) / 1024) * 2199; scale /= th->th_counter->tc_frequency; th->th_scale = scale * 2; @@ -751,7 +753,7 @@ sysctl_tc(int *name, u_int namelen, void *oldp, size_t *oldlenp, } /* - * Skew the timehands according to any adjfreq(2)/adjtime(2) adjustments. + * Skew the timehands according to any adjtime(2) adjustment. */ void ntp_update_second(struct timehands *th) @@ -766,7 +768,6 @@ ntp_update_second(struct timehands *th) adj = MAX(-5000, th->th_adjtimedelta); th->th_adjtimedelta -= adj; th->th_adjustment = (adj * 1000) << 32; - th->th_adjustment += th->th_counter->tc_freq_adj; } void |