Commit 09edea4f authored Aug 10, 2015 by Nathan Lynch Committed by Russell King Aug 11, 2015

ARM: 8410/1: VDSO: fix coarse clock monotonicity regression



Since 906c5557 ("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.

Cc: stable@vger.kernel.org
Fixes: 906c5557 ("timekeeping: Copy the shadow-timekeeper over the real timekeeper last")
Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

parent e83dd377

arch/arm/kernel/vdso.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -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;