timekeeping: Fix 1ns/tick drift with GENERIC_TIME_VSYSCALL_OLD

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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>

...

This commit is contained in:

Thomas Graziadei 2016-05-31 15:06:06 +02:00 • committed by John Stultz

parent 0fb71d340d

commit 0209b93756

1 changed files with 6 additions and 4 deletions

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kernel/time/timekeeping.c

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