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    Subject[ 34/37] timekeeping: Provide hrtimer update function
    Date
    From: Greg KH <gregkh@linuxfoundation.org>

    3.4-stable review patch. If anyone has any objections, please let me know.

    ------------------


    From: Thomas Gleixner <tglx@linutronix.de>

    This is a backport of f6c06abfb3972ad4914cef57d8348fcb2932bc3b

    To finally fix the infamous leap second issue and other race windows
    caused by functions which change the offsets between the various time
    bases (CLOCK_MONOTONIC, CLOCK_REALTIME and CLOCK_BOOTTIME) we need a
    function which atomically gets the current monotonic time and updates
    the offsets of CLOCK_REALTIME and CLOCK_BOOTTIME with minimalistic
    overhead. The previous patch which provides ktime_t offsets allows us
    to make this function almost as cheap as ktime_get() which is going to
    be replaced in hrtimer_interrupt().

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Ingo Molnar <mingo@kernel.org>
    Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Acked-by: Prarit Bhargava <prarit@redhat.com>
    Signed-off-by: John Stultz <johnstul@us.ibm.com>
    Link: http://lkml.kernel.org/r/1341960205-56738-7-git-send-email-johnstul@us.ibm.com
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Prarit Bhargava <prarit@redhat.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: John Stultz <johnstul@us.ibm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    include/linux/hrtimer.h | 1 +
    kernel/time/timekeeping.c | 34 ++++++++++++++++++++++++++++++++++
    2 files changed, 35 insertions(+)

    --- a/include/linux/hrtimer.h
    +++ b/include/linux/hrtimer.h
    @@ -327,6 +327,7 @@ extern ktime_t ktime_get(void);
    extern ktime_t ktime_get_real(void);
    extern ktime_t ktime_get_boottime(void);
    extern ktime_t ktime_get_monotonic_offset(void);
    +extern ktime_t ktime_get_update_offsets(ktime_t *offs_real, ktime_t *offs_boot);

    DECLARE_PER_CPU(struct tick_device, tick_cpu_device);

    --- a/kernel/time/timekeeping.c
    +++ b/kernel/time/timekeeping.c
    @@ -1273,6 +1273,40 @@ void get_xtime_and_monotonic_and_sleep_o
    } while (read_seqretry(&timekeeper.lock, seq));
    }

    +#ifdef CONFIG_HIGH_RES_TIMERS
    +/**
    + * ktime_get_update_offsets - hrtimer helper
    + * @offs_real: pointer to storage for monotonic -> realtime offset
    + * @offs_boot: pointer to storage for monotonic -> boottime offset
    + *
    + * Returns current monotonic time and updates the offsets
    + * Called from hrtimer_interupt() or retrigger_next_event()
    + */
    +ktime_t ktime_get_update_offsets(ktime_t *offs_real, ktime_t *offs_boot)
    +{
    + ktime_t now;
    + unsigned int seq;
    + u64 secs, nsecs;
    +
    + do {
    + seq = read_seqbegin(&timekeeper.lock);
    +
    + secs = timekeeper.xtime.tv_sec;
    + nsecs = timekeeper.xtime.tv_nsec;
    + nsecs += timekeeping_get_ns();
    + /* If arch requires, add in gettimeoffset() */
    + nsecs += arch_gettimeoffset();
    +
    + *offs_real = timekeeper.offs_real;
    + *offs_boot = timekeeper.offs_boot;
    + } while (read_seqretry(&timekeeper.lock, seq));
    +
    + now = ktime_add_ns(ktime_set(secs, 0), nsecs);
    + now = ktime_sub(now, *offs_real);
    + return now;
    +}
    +#endif
    +
    /**
    * ktime_get_monotonic_offset() - get wall_to_monotonic in ktime_t format
    */



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