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_ly...@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.dea...@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.
--
Catalin
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
