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authorThomas Graziadei <thomas.graziadei@omicronenergy.com>2016-05-31 15:06:06 +0200
committerJohn Stultz <john.stultz@linaro.org>2016-06-20 12:46:45 -0700
commit0209b937569a133dedfe930cdfff3a0d1d68c9e9 (patch)
treea35461164f667e343c98731f7f781d3e0b422890 /kernel
parent0fb71d340d355156818bb53eb36ae79a3f88bda9 (diff)
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')
-rw-r--r--kernel/time/timekeeping.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 479d25cd3d4f..a196e08324e7 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)