• John Stultz's avatar
    hrtimer: Update hrtimer base offsets each hrtimer_interrupt · 5baefd6d
    John Stultz authored
    The update of the hrtimer base offsets on all cpus cannot be made
    atomically from the timekeeper.lock held and interrupt disabled region
    as smp function calls are not allowed there.
    clock_was_set(), which enforces the update on all cpus, is called
    either from preemptible process context in case of do_settimeofday()
    or from the softirq context when the offset modification happened in
    the timer interrupt itself due to a leap second.
    In both cases there is a race window for an hrtimer interrupt between
    dropping timekeeper lock, enabling interrupts and clock_was_set()
    issuing the updates. Any interrupt which arrives in that window will
    see the new time but operate on stale offsets.
    So we need to make sure that an hrtimer interrupt always sees a
    consistent state of time and offsets.
    ktime_get_update_offsets() allows us to get the current monotonic time
    and update the per cpu hrtimer base offsets from hrtimer_interrupt()
    to capture a consistent state of monotonic time and the offsets. The
    function replaces the existing ktime_get() calls in hrtimer_interrupt().
    The overhead of the new function vs. ktime_get() is minimal as it just
    adds two store operations.
    This ensures that any changes to realtime or boottime offsets are
    noticed and stored into the per-cpu hrtimer base structures, prior to
    any hrtimer expiration and guarantees that timers are not expired early.
    Signed-off-by: default avatarJohn Stultz <johnstul@us.ibm.com>
    Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
    Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Acked-by: default avatarPrarit Bhargava <prarit@redhat.com>
    Cc: stable@vger.kernel.org
    Link: http://lkml.kernel.org/r/1341960205-56738-8-git-send-email-johnstul@us.ibm.comSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
hrtimer.c 47 KB