linux-kernel - Re: [patch 7/7] posix-timers: Prepare for PREEMPT

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Date:   Wed, 31 Jul 2019 11:49:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Julia Cartwright <julia@...com>
Subject: Re: [patch 7/7] posix-timers: Prepare for PREEMPT_RT

On Wed, Jul 31, 2019 at 12:33:55AM +0200, Thomas Gleixner wrote:
> +static struct k_itimer *timer_wait_running(struct k_itimer *timer,
> +					   unsigned long *flags)
> +{
> +	const struct k_clock *kc = READ_ONCE(timer->kclock);
> +	timer_t timer_id = READ_ONCE(timer->it_id);
> +
> +	/* Prevent kfree(timer) after dropping the lock */
> +	rcu_read_lock();
> +	unlock_timer(timer, *flags);
> +
> +	if (kc->timer_arm == common_hrtimer_arm)
> +		hrtimer_cancel_wait_running(&timer->it.real.timer);
> +	else if (kc == &alarm_clock)
> +		hrtimer_cancel_wait_running(&timer->it.alarm.alarmtimer.timer);

	else WARN();

> +	rcu_read_unlock();
> +
> +	/* Relock the timer. It might be not longer hashed. */
> +	return lock_timer(timer_id, flags);
> +}