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arm64: VDSO: fix coarse clock monotonicity regression 

Since 906c55579a ("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>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Nathan Lynch 2015-08-07 21:03:23 -05:00 committed by Catalin Marinas
parent f7644cbfcd
commit 878854a374
1 changed files with 3 additions and 4 deletions
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7
arch/arm64/kernel/vdso.c
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@ -199,16 +199,15 @@ up_fail:
*/ */
void update_vsyscall(struct timekeeper *tk) void update_vsyscall(struct timekeeper *tk)
{ {
struct timespec xtime_coarse;
u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter"); u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter");
++vdso_data->tb_seq_count; ++vdso_data->tb_seq_count;
smp_wmb(); smp_wmb();
xtime_coarse = __current_kernel_time();
vdso_data->use_syscall = use_syscall; vdso_data->use_syscall = use_syscall;
vdso_data->xtime_coarse_sec = xtime_coarse.tv_sec; vdso_data->xtime_coarse_sec = tk->xtime_sec;
vdso_data->xtime_coarse_nsec = xtime_coarse.tv_nsec; 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_sec = tk->wall_to_monotonic.tv_sec;
vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec; vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec;