[ Upstream commit fdc6bae940ee9eb869e493990540098b8c0fd6ab ]
The ADJ_TAI adjtimex mode sets the TAI-UTC offset of the system clock. It is typically set by NTP/PTP implementations and it is automatically updated by the kernel on leap seconds. The initial value is zero (which applications may interpret as unknown), but this value cannot be set by adjtimex. This limitation seems to go back to the original "nanokernel" implementation by David Mills.
Change the ADJ_TAI check to accept zero as a valid TAI-UTC offset in order to allow setting it back to the initial value.
Fixes: 153b5d054ac2 ("ntp: support for TAI") Suggested-by: Ondrej Mosnacek omosnace@redhat.com Signed-off-by: Miroslav Lichvar mlichvar@redhat.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: John Stultz john.stultz@linaro.org Cc: Richard Cochran richardcochran@gmail.com Cc: Prarit Bhargava prarit@redhat.com Link: https://lkml.kernel.org/r/20190417084833.7401-1-mlichvar@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/time/ntp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c index 99e03bec68e4..4bb9b66338be 100644 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -640,7 +640,7 @@ static inline void process_adjtimex_modes(struct timex *txc, time_constant = max(time_constant, 0l); }
- if (txc->modes & ADJ_TAI && txc->constant > 0) + if (txc->modes & ADJ_TAI && txc->constant >= 0) *time_tai = txc->constant;
if (txc->modes & ADJ_OFFSET)