Messages in this thread | | | Date | Wed, 12 Aug 2015 13:00:04 -0700 | Subject | Re: [PATCH v2] ARM: VDSO: fix coarse clock monotonicity regression | From | John Stultz <> |
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On Mon, Aug 10, 2015 at 8:46 AM, Nathan Lynch <nathan_lynch@mentor.com> wrote: > Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the > real timekeeper last") it has become possible on ARM to:
Apologies I didn't catch that the core change caused a regression for ARM. Though fixing the ARM vdso logic in this way is a good idea to avoid future problems.
> - Obtain a CLOCK_MONOTONIC_COARSE or CLOCK_REALTIME_COARSE timestamp > via syscall. > - Subsequently obtain a timestamp for the same clock ID via VDSO which > predates the first timestamp (by one jiffy). > > This is because ARM's update_vsyscall is deriving the coarse time > using the __current_kernel_time interface, when it should really be > using the timekeeper object provided to it by the timekeeping core. > It happened to work before only because __current_kernel_time would > access the same timekeeper object which had been passed to > update_vsyscall. This is no longer the case. > > Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com> > --- > > Changes since v1: > - Add u32 cast to nsec calculation. > > arch/arm/kernel/vdso.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/arch/arm/kernel/vdso.c b/arch/arm/kernel/vdso.c > index efe17dd9b921..54a5aeab988d 100644 > --- a/arch/arm/kernel/vdso.c > +++ b/arch/arm/kernel/vdso.c > @@ -296,7 +296,6 @@ static bool tk_is_cntvct(const struct timekeeper *tk) > */ > void update_vsyscall(struct timekeeper *tk) > { > - struct timespec xtime_coarse; > struct timespec64 *wtm = &tk->wall_to_monotonic; > > if (!cntvct_ok) { > @@ -308,10 +307,10 @@ void update_vsyscall(struct timekeeper *tk) > > vdso_write_begin(vdso_data); > > - xtime_coarse = __current_kernel_time(); > vdso_data->tk_is_cntvct = tk_is_cntvct(tk); > - vdso_data->xtime_coarse_sec = xtime_coarse.tv_sec; > - vdso_data->xtime_coarse_nsec = xtime_coarse.tv_nsec; > + vdso_data->xtime_coarse_sec = tk->xtime_sec; > + vdso_data->xtime_coarse_nsec = (u32)(tk->tkr_mono.xtime_nsec >> > + tk->tkr_mono.shift); > vdso_data->wtm_clock_sec = wtm->tv_sec; > vdso_data->wtm_clock_nsec = wtm->tv_nsec;
Acked-by: John Stultz <john.stultz@linaro.org>
thanks -john
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