| Message ID | 1438999403-5770-3-git-send-email-nathan_lynch@mentor.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Nathan, On Sat, Aug 08, 2015 at 03:03:23AM +0100, Nathan Lynch wrote: > Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the > real timekeeper last") it has become possible on arm64 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 arm64'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> > --- > arch/arm64/kernel/vdso.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c > index ec37ab3f524f..97bc68f4c689 100644 > --- a/arch/arm64/kernel/vdso.c > +++ b/arch/arm64/kernel/vdso.c > @@ -199,16 +199,15 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, > */ > void update_vsyscall(struct timekeeper *tk) > { > - struct timespec xtime_coarse; > u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter"); > > ++vdso_data->tb_seq_count; > smp_wmb(); > > - xtime_coarse = __current_kernel_time(); > vdso_data->use_syscall = use_syscall; > - 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 = tk->tkr_mono.xtime_nsec >> > + tk->tkr_mono.shift; > vdso_data->wtm_clock_sec = tk->wall_to_monotonic.tv_sec; > vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec; Looks good, Acked-by: Will Deacon <will.deacon@arm.com> There's probably still time for Catalin to pick this up for 4.2. Will
On Mon, Aug 10, 2015 at 10:22:53AM +0100, Will Deacon wrote: > On Sat, Aug 08, 2015 at 03:03:23AM +0100, Nathan Lynch wrote: > > Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the > > real timekeeper last") it has become possible on arm64 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 arm64'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> > > --- > > arch/arm64/kernel/vdso.c | 7 +++---- > > 1 file changed, 3 insertions(+), 4 deletions(-) > > > > diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c > > index ec37ab3f524f..97bc68f4c689 100644 > > --- a/arch/arm64/kernel/vdso.c > > +++ b/arch/arm64/kernel/vdso.c > > @@ -199,16 +199,15 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, > > */ > > void update_vsyscall(struct timekeeper *tk) > > { > > - struct timespec xtime_coarse; > > u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter"); > > > > ++vdso_data->tb_seq_count; > > smp_wmb(); > > > > - xtime_coarse = __current_kernel_time(); > > vdso_data->use_syscall = use_syscall; > > - 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 = tk->tkr_mono.xtime_nsec >> > > + tk->tkr_mono.shift; > > vdso_data->wtm_clock_sec = tk->wall_to_monotonic.tv_sec; > > vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec; > > Looks good, > > Acked-by: Will Deacon <will.deacon@arm.com> > > There's probably still time for Catalin to pick this up for 4.2. Applied, I'll send a pull request today/tomorrow. Thanks.
On Fri, Aug 7, 2015 at 7:03 PM, Nathan Lynch <nathan_lynch@mentor.com> wrote: > Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the > real timekeeper last") it has become possible on arm64 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 arm64'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> > --- > arch/arm64/kernel/vdso.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c > index ec37ab3f524f..97bc68f4c689 100644 > --- a/arch/arm64/kernel/vdso.c > +++ b/arch/arm64/kernel/vdso.c > @@ -199,16 +199,15 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, > */ > void update_vsyscall(struct timekeeper *tk) > { > - struct timespec xtime_coarse; > u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter"); > > ++vdso_data->tb_seq_count; > smp_wmb(); > > - xtime_coarse = __current_kernel_time(); > vdso_data->use_syscall = use_syscall; > - 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 = tk->tkr_mono.xtime_nsec >> > + tk->tkr_mono.shift; > vdso_data->wtm_clock_sec = tk->wall_to_monotonic.tv_sec; > vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec; > (Sorry for the slow response, I've been out on vacation). If its worth anything now: Acked-by: John Stultz <john.stultz@linaro.org> thanks -john
diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c index ec37ab3f524f..97bc68f4c689 100644 --- a/arch/arm64/kernel/vdso.c +++ b/arch/arm64/kernel/vdso.c @@ -199,16 +199,15 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, */ void update_vsyscall(struct timekeeper *tk) { - struct timespec xtime_coarse; u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter"); ++vdso_data->tb_seq_count; smp_wmb(); - xtime_coarse = __current_kernel_time(); vdso_data->use_syscall = use_syscall; - 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 = tk->tkr_mono.xtime_nsec >> + tk->tkr_mono.shift; vdso_data->wtm_clock_sec = tk->wall_to_monotonic.tv_sec; vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec;
Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the real timekeeper last") it has become possible on arm64 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 arm64'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> --- arch/arm64/kernel/vdso.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)