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| author | Thomas Graziadei <thomas.graziadei@omicronenergy.com> | 2016-05-31 15:06:06 +0200 |
|---|---|---|
| committer | John Stultz <john.stultz@linaro.org> | 2016-06-20 12:46:45 -0700 |
| commit | 0209b937569a133dedfe930cdfff3a0d1d68c9e9 (patch) | |
| tree | a35461164f667e343c98731f7f781d3e0b422890 /kernel/time | |
| parent | 0fb71d340d355156818bb53eb36ae79a3f88bda9 (diff) | |
| download | linux-0-day-0209b937569a133dedfe930cdfff3a0d1d68c9e9.tar.gz linux-0-day-0209b937569a133dedfe930cdfff3a0d1d68c9e9.tar.xz | |
timekeeping: Fix 1ns/tick drift with GENERIC_TIME_VSYSCALL_OLD
The user notices the problem in a raw and real time drift, calling
clock_gettime with CLOCK_REALTIME / CLOCK_MONOTONIC_RAW on a system
with no ntp correction taking place (no ntpd or ptp stuff running).
The problem is, that old_vsyscall_fixup adds an extra 1ns even though
xtime_nsec is already held in full nsecs and the remainder in this
case is 0. Do the rounding up buisness only if needed.
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Thomas Graziadei <thomas.graziadei@omicronenergy.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'kernel/time')
| -rw-r--r-- | kernel/time/timekeeping.c | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 479d25cd3d4ff..a196e08324e76 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -480,10 +480,12 @@ static inline void old_vsyscall_fixup(struct timekeeper *tk) * users are removed, this can be killed. */ remainder = tk->tkr_mono.xtime_nsec & ((1ULL << tk->tkr_mono.shift) - 1); - tk->tkr_mono.xtime_nsec -= remainder; - tk->tkr_mono.xtime_nsec += 1ULL << tk->tkr_mono.shift; - tk->ntp_error += remainder << tk->ntp_error_shift; - tk->ntp_error -= (1ULL << tk->tkr_mono.shift) << tk->ntp_error_shift; + if (remainder != 0) { + tk->tkr_mono.xtime_nsec -= remainder; + tk->tkr_mono.xtime_nsec += 1ULL << tk->tkr_mono.shift; + tk->ntp_error += remainder << tk->ntp_error_shift; + tk->ntp_error -= (1ULL << tk->tkr_mono.shift) << tk->ntp_error_shift; + } } #else #define old_vsyscall_fixup(tk) |