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Commit 21e460ea authored by Nathan Lynch's avatar Nathan Lynch Committed by Mark Salyzyn
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UPSTREAM: ARM: 8410/1: VDSO: fix coarse clock monotonicity regression 



(cherry pick from commit 09edea4f8fdeb4e292b80d493296070f5ec64e6e)

Since 906c55579a63 ("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: 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the real timekeeper last")
Signed-off-by: default avatarNathan Lynch <nathan_lynch@mentor.com>
Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
Bug: 20045882
Bug: 19198045
Change-Id: If1eb4396a1e33a5127d49a2fd0ea83e09e4214b3
parent c93a16f5

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;