| Message ID | 1439221592-31875-1-git-send-email-nathan_lynch@mentor.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Aug 10, 2015 at 04:46:32PM +0100, Nathan Lynch wrote: > Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the > real timekeeper last") it has become possible on ARM to: > > - 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. Acked-by: Will Deacon <will.deacon@arm.com> Probably best sticking it into Russell's patch system with a Cc stable in case it doesn't make it for 4.2. Will > 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; > > -- > 2.1.0 >
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
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;
Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the real timekeeper last") it has become possible on ARM to: - 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(-)