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    Subject[tip:timers/core] itimers: Prepare for PREEMPT_RT
    Commit-ID:  cab46ec655eec1b5dbb0c17a25e19f67c539f00b
    Gitweb: https://git.kernel.org/tip/cab46ec655eec1b5dbb0c17a25e19f67c539f00b
    Author: Anna-Maria Gleixner <anna-maria@linutronix.de>
    AuthorDate: Wed, 31 Jul 2019 00:33:51 +0200
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Thu, 1 Aug 2019 17:46:41 +0200

    itimers: Prepare for PREEMPT_RT

    Use the hrtimer_cancel_wait_running() synchronization mechanism to prevent
    priority inversion and live locks on PREEMPT_RT.

    As a benefit the retry loop gains the missing cpu_relax() on !RT.

    [ tglx: Split out of combo patch ]

    Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20190730223828.690771827@linutronix.de

    ---
    kernel/time/itimer.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
    index 02068b2d5862..9d26fd4ba4c0 100644
    --- a/kernel/time/itimer.c
    +++ b/kernel/time/itimer.c
    @@ -213,6 +213,7 @@ again:
    /* We are sharing ->siglock with it_real_fn() */
    if (hrtimer_try_to_cancel(timer) < 0) {
    spin_unlock_irq(&tsk->sighand->siglock);
    + hrtimer_cancel_wait_running(timer);
    goto again;
    }
    expires = timeval_to_ktime(value->it_value);
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