Commit 878854a3 authored Aug 07, 2015 by Nathan Lynch Committed by Catalin Marinas Aug 10, 2015

arm64: VDSO: fix coarse clock monotonicity regression



Since 906c5557 ("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>

parent f7644cbf

arch/arm64/kernel/vdso.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -199,16 +199,15 @@ up_fail:
		*/
		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;

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