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    Subject[tip:timers/core] clocksource: Remove kthread
    Commit-ID:  7197e77abcb65a71d0b21d67beb24f153a96055e
    Gitweb: https://git.kernel.org/tip/7197e77abcb65a71d0b21d67beb24f153a96055e
    Author: Peter Zijlstra <peterz@infradead.org>
    AuthorDate: Mon, 30 Apr 2018 12:00:15 +0200
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Wed, 2 May 2018 16:11:46 +0200

    clocksource: Remove kthread

    The clocksource watchdog uses a work to spawn a kthread to run the
    watchdog. That is about as silly as it sounds, run the watchdog
    directly from the work.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Cc: len.brown@intel.com
    Cc: rjw@rjwysocki.net
    Cc: diego.viola@gmail.com
    Cc: rui.zhang@intel.com
    Link: https://lkml.kernel.org/r/20180430100344.713862818@infradead.org

    ---
    kernel/time/clocksource.c | 31 ++++++++++---------------------
    1 file changed, 10 insertions(+), 21 deletions(-)

    diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
    index 84f37420fcf5..56fd2239674f 100644
    --- a/kernel/time/clocksource.c
    +++ b/kernel/time/clocksource.c
    @@ -129,31 +129,19 @@ static void inline clocksource_watchdog_unlock(unsigned long *flags)
    spin_unlock_irqrestore(&watchdog_lock, *flags);
    }

    -static int clocksource_watchdog_kthread(void *data);
    -static void __clocksource_change_rating(struct clocksource *cs, int rating);
    -
    /*
    * Interval: 0.5sec Threshold: 0.0625s
    */
    #define WATCHDOG_INTERVAL (HZ >> 1)
    #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)

    -static void clocksource_watchdog_work(struct work_struct *work)
    -{
    - /*
    - * If kthread_run fails the next watchdog scan over the
    - * watchdog_list will find the unstable clock again.
    - */
    - kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
    -}
    -
    static void __clocksource_unstable(struct clocksource *cs)
    {
    cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
    cs->flags |= CLOCK_SOURCE_UNSTABLE;

    /*
    - * If the clocksource is registered clocksource_watchdog_kthread() will
    + * If the clocksource is registered clocksource_watchdog_work() will
    * re-rate and re-select.
    */
    if (list_empty(&cs->list)) {
    @@ -164,7 +152,7 @@ static void __clocksource_unstable(struct clocksource *cs)
    if (cs->mark_unstable)
    cs->mark_unstable(cs);

    - /* kick clocksource_watchdog_kthread() */
    + /* kick clocksource_watchdog_work() */
    if (finished_booting)
    schedule_work(&watchdog_work);
    }
    @@ -174,7 +162,7 @@ static void __clocksource_unstable(struct clocksource *cs)
    * @cs: clocksource to be marked unstable
    *
    * This function is called by the x86 TSC code to mark clocksources as unstable;
    - * it defers demotion and re-selection to a kthread.
    + * it defers demotion and re-selection to a work.
    */
    void clocksource_mark_unstable(struct clocksource *cs)
    {
    @@ -399,7 +387,9 @@ static void clocksource_dequeue_watchdog(struct clocksource *cs)
    }
    }

    -static int __clocksource_watchdog_kthread(void)
    +static void __clocksource_change_rating(struct clocksource *cs, int rating);
    +
    +static int __clocksource_watchdog_work(void)
    {
    struct clocksource *cs, *tmp;
    unsigned long flags;
    @@ -424,13 +414,12 @@ static int __clocksource_watchdog_kthread(void)
    return select;
    }

    -static int clocksource_watchdog_kthread(void *data)
    +static void clocksource_watchdog_work(struct work_struct *work)
    {
    mutex_lock(&clocksource_mutex);
    - if (__clocksource_watchdog_kthread())
    + if (__clocksource_watchdog_work())
    clocksource_select();
    mutex_unlock(&clocksource_mutex);
    - return 0;
    }

    static bool clocksource_is_watchdog(struct clocksource *cs)
    @@ -449,7 +438,7 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs)
    static void clocksource_select_watchdog(bool fallback) { }
    static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
    static inline void clocksource_resume_watchdog(void) { }
    -static inline int __clocksource_watchdog_kthread(void) { return 0; }
    +static inline int __clocksource_watchdog_work(void) { return 0; }
    static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
    void clocksource_mark_unstable(struct clocksource *cs) { }

    @@ -683,7 +672,7 @@ static int __init clocksource_done_booting(void)
    /*
    * Run the watchdog first to eliminate unstable clock sources
    */
    - __clocksource_watchdog_kthread();
    + __clocksource_watchdog_work();
    clocksource_select();
    mutex_unlock(&clocksource_mutex);
    return 0;
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