ARM: 8410/1: VDSO: fix coarse clock monotonicity regression
authorNathan Lynch <nathan_lynch@mentor.com>
Mon, 10 Aug 2015 16:36:06 +0000 (17:36 +0100)
committerRussell King <rmk+kernel@arm.linux.org.uk>
Tue, 11 Aug 2015 12:42:44 +0000 (13:42 +0100)
commit09edea4f8fdeb4e292b80d493296070f5ec64e6e
tree4215bd594495bc36545a4e092474977ebc44a1e8
parente83dd3770021910293edea6fb2dc2fa306b1bf34
ARM: 8410/1: VDSO: fix coarse clock monotonicity regression

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: 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>
arch/arm/kernel/vdso.c