• Will Deacon's avatar
    arm64/vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW · dbb236c1
    Will Deacon authored
    Recently vDSO support for CLOCK_MONOTONIC_RAW was added in
    49eea433 ("arm64: Add support for CLOCK_MONOTONIC_RAW in
    clock_gettime() vDSO"). Noticing that the core timekeeping code
    never set tkr_raw.xtime_nsec, the vDSO implementation didn't
    bother exposing it via the data page and instead took the
    unshifted tk->raw_time.tv_nsec value which was then immediately
    shifted left in the vDSO code.
    
    Unfortunately, by accellerating the MONOTONIC_RAW clockid, it
    uncovered potential 1ns time inconsistencies caused by the
    timekeeping core not handing sub-ns resolution.
    
    Now that the core code has been fixed and is actually setting
    tkr_raw.xtime_nsec, we need to take that into account in the
    vDSO by adding it to the shifted raw_time value, in order to
    fix the user-visible inconsistency. Rather than do that at each
    use (and expand the data page in the process), instead perform
    the shift/addition operation when populating the data page and
    remove the shift from the vDSO code entirely.
    
    [jstultz: minor whitespace tweak, tried to improve commit
     message to make it more clear this fixes a regression]
    Reported-by: default avatarJohn Stultz <john.stultz@linaro.org>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
    Tested-by: default avatarDaniel Mentz <danielmentz@google.com>
    Acked-by: default avatarKevin Brodsky <kevin.brodsky@arm.com>
    Cc: Prarit Bhargava <prarit@redhat.com>
    Cc: Richard Cochran <richardcochran@gmail.com>
    Cc: Stephen Boyd <stephen.boyd@linaro.org>
    Cc: "stable #4 . 8+" <stable@vger.kernel.org>
    Cc: Miroslav Lichvar <mlichvar@redhat.com>
    Link: http://lkml.kernel.org/r/1496965462-20003-4-git-send-email-john.stultz@linaro.orgSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    dbb236c1
gettimeofday.S 8.01 KB