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    Subject[PATCH 1/2] time: Serialize calls to 'clockevents_update_freq' in the timing core
    Date
    From: Thomas Gleixner <tglx@linutronix.de>

    We can identify the broadcast device in the core and serialize all
    callers including interrupts on a different CPU against the update.
    Also, disabling interrupts is moved into the core allowing callers to
    leave interrutps enabled when calling clockevents_update_freq().

    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
    ---
    kernel/time/clockevents.c | 29 ++++++++++++++++++++++-------
    kernel/time/tick-broadcast.c | 25 +++++++++++++++++++------
    kernel/time/tick-internal.h | 4 ++++
    3 files changed, 45 insertions(+), 13 deletions(-)

    diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
    index 086ad6043bcb..641d91003a45 100644
    --- a/kernel/time/clockevents.c
    +++ b/kernel/time/clockevents.c
    @@ -439,6 +439,16 @@ void clockevents_config_and_register(struct clock_event_device *dev,
    }
    EXPORT_SYMBOL_GPL(clockevents_config_and_register);

    +int __clockevents_update_freq(struct clock_event_device *dev, u32 freq)
    +{
    + clockevents_config(dev, freq);
    +
    + if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
    + return 0;
    +
    + return clockevents_program_event(dev, dev->next_event, false);
    +}
    +
    /**
    * clockevents_update_freq - Update frequency and reprogram a clock event device.
    * @dev: device to modify
    @@ -446,17 +456,22 @@ EXPORT_SYMBOL_GPL(clockevents_config_and_register);
    *
    * Reconfigure and reprogram a clock event device in oneshot
    * mode. Must be called on the cpu for which the device delivers per
    - * cpu timer events with interrupts disabled! Returns 0 on success,
    - * -ETIME when the event is in the past.
    + * cpu timer events. If called for the broadcast device the core takes
    + * care of serialization.
    + *
    + * Returns 0 on success, -ETIME when the event is in the past.
    */
    int clockevents_update_freq(struct clock_event_device *dev, u32 freq)
    {
    - clockevents_config(dev, freq);
    -
    - if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
    - return 0;
    + unsigned long flags;
    + int ret;

    - return clockevents_program_event(dev, dev->next_event, false);
    + local_irq_save(flags);
    + ret = tick_broadcast_update_freq(dev, freq);
    + if (ret == -ENODEV)
    + ret = __clockevents_update_freq(dev, freq);
    + local_irq_restore(flags);
    + return ret;
    }

    /*
    diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
    index 9532690daaa9..63a33b33fc4e 100644
    --- a/kernel/time/tick-broadcast.c
    +++ b/kernel/time/tick-broadcast.c
    @@ -120,6 +120,19 @@ int tick_is_broadcast_device(struct clock_event_device *dev)
    return (dev && tick_broadcast_device.evtdev == dev);
    }

    +int tick_broadcast_update_freq(struct clock_event_device *dev, u32 freq)
    +{
    + int ret = -ENODEV;
    +
    + if (tick_is_broadcast_device(dev)) {
    + raw_spin_lock(&tick_broadcast_lock);
    + ret = __clockevents_update_freq(dev, freq);
    + raw_spin_unlock(&tick_broadcast_lock);
    + }
    + return ret;
    +}
    +
    +
    static void err_broadcast(const struct cpumask *mask)
    {
    pr_crit_once("Failed to broadcast timer tick. Some CPUs may be unresponsive.\n");
    @@ -272,12 +285,8 @@ static void tick_do_broadcast(struct cpumask *mask)
    */
    static void tick_do_periodic_broadcast(void)
    {
    - raw_spin_lock(&tick_broadcast_lock);
    -
    cpumask_and(tmpmask, cpu_online_mask, tick_broadcast_mask);
    tick_do_broadcast(tmpmask);
    -
    - raw_spin_unlock(&tick_broadcast_lock);
    }

    /*
    @@ -287,13 +296,15 @@ static void tick_handle_periodic_broadcast(struct clock_event_device *dev)
    {
    ktime_t next;

    + raw_spin_lock(&tick_broadcast_lock);
    +
    tick_do_periodic_broadcast();

    /*
    * The device is in periodic mode. No reprogramming necessary:
    */
    if (dev->mode == CLOCK_EVT_MODE_PERIODIC)
    - return;
    + goto unlock;

    /*
    * Setup the next period for devices, which do not have
    @@ -306,9 +317,11 @@ static void tick_handle_periodic_broadcast(struct clock_event_device *dev)
    next = ktime_add(next, tick_period);

    if (!clockevents_program_event(dev, next, false))
    - return;
    + goto unlock;
    tick_do_periodic_broadcast();
    }
    +unlock:
    + raw_spin_unlock(&tick_broadcast_lock);
    }

    /*
    diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
    index 18e71f7fbc2a..22fd431a02eb 100644
    --- a/kernel/time/tick-internal.h
    +++ b/kernel/time/tick-internal.h
    @@ -111,6 +111,7 @@ extern int tick_resume_broadcast(void);
    extern void tick_broadcast_init(void);
    extern void
    tick_set_periodic_handler(struct clock_event_device *dev, int broadcast);
    +int tick_broadcast_update_freq(struct clock_event_device *dev, u32 freq);

    #else /* !BROADCAST */

    @@ -133,6 +134,8 @@ static inline void tick_shutdown_broadcast(unsigned int *cpup) { }
    static inline void tick_suspend_broadcast(void) { }
    static inline int tick_resume_broadcast(void) { return 0; }
    static inline void tick_broadcast_init(void) { }
    +static inline int tick_broadcast_update_freq(struct clock_event_device *dev,
    + u32 freq) { return -ENODEV; }

    /*
    * Set the periodic handler in non broadcast mode
    @@ -154,4 +157,5 @@ static inline int tick_device_is_functional(struct clock_event_device *dev)

    #endif

    +int __clockevents_update_freq(struct clock_event_device *dev, u32 freq);
    extern void do_timer(unsigned long ticks);
    --
    1.8.5.1


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