rtc: Fix hrtimer deadlock
Ben reported a lockup related to rtc. The lockup happens due to: CPU0 CPU1 rtc_irq_set_state() __run_hrtimer() spin_lock_irqsave(&rtc->irq_task_lock) rtc_handle_legacy_irq(); spin_lock(&rtc->irq_task_lock); hrtimer_cancel() while (callback_running); So the running callback never finishes as it's blocked on rtc->irq_task_lock. Use hrtimer_try_to_cancel() instead and drop rtc->irq_task_lock while waiting for the callback. Fix this for both rtc_irq_set_state() and rtc_irq_set_freq(). Cc: stable@kernel.org Reported-by: Ben Greear <greearb@candelatech.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: John Stultz <john.stultz@linaro.org>
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53cc2820ac
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3c8bb90efb
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@ -636,6 +636,29 @@ void rtc_irq_unregister(struct rtc_device *rtc, struct rtc_task *task)
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}
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EXPORT_SYMBOL_GPL(rtc_irq_unregister);
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static int rtc_update_hrtimer(struct rtc_device *rtc, int enabled)
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{
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/*
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* We always cancel the timer here first, because otherwise
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* we could run into BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
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* when we manage to start the timer before the callback
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* returns HRTIMER_RESTART.
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*
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* We cannot use hrtimer_cancel() here as a running callback
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* could be blocked on rtc->irq_task_lock and hrtimer_cancel()
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* would spin forever.
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*/
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if (hrtimer_try_to_cancel(&rtc->pie_timer) < 0)
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return -1;
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if (enabled) {
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ktime_t period = ktime_set(0, NSEC_PER_SEC / rtc->irq_freq);
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hrtimer_start(&rtc->pie_timer, period, HRTIMER_MODE_REL);
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}
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return 0;
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}
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/**
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* rtc_irq_set_state - enable/disable 2^N Hz periodic IRQs
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* @rtc: the rtc device
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@ -651,24 +674,21 @@ int rtc_irq_set_state(struct rtc_device *rtc, struct rtc_task *task, int enabled
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int err = 0;
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unsigned long flags;
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retry:
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spin_lock_irqsave(&rtc->irq_task_lock, flags);
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if (rtc->irq_task != NULL && task == NULL)
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err = -EBUSY;
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if (rtc->irq_task != task)
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err = -EACCES;
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if (err)
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goto out;
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if (enabled) {
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ktime_t period = ktime_set(0, NSEC_PER_SEC/rtc->irq_freq);
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hrtimer_start(&rtc->pie_timer, period, HRTIMER_MODE_REL);
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} else {
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hrtimer_cancel(&rtc->pie_timer);
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if (!err) {
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if (rtc_update_hrtimer(rtc, enabled) < 0) {
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spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
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cpu_relax();
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goto retry;
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}
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rtc->pie_enabled = enabled;
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}
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rtc->pie_enabled = enabled;
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out:
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spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
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return err;
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}
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EXPORT_SYMBOL_GPL(rtc_irq_set_state);
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@ -690,20 +710,18 @@ int rtc_irq_set_freq(struct rtc_device *rtc, struct rtc_task *task, int freq)
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if (freq <= 0)
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return -EINVAL;
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retry:
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spin_lock_irqsave(&rtc->irq_task_lock, flags);
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if (rtc->irq_task != NULL && task == NULL)
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err = -EBUSY;
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if (rtc->irq_task != task)
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err = -EACCES;
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if (err == 0) {
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if (!err) {
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rtc->irq_freq = freq;
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if (rtc->pie_enabled) {
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ktime_t period;
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hrtimer_cancel(&rtc->pie_timer);
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period = ktime_set(0, NSEC_PER_SEC/rtc->irq_freq);
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hrtimer_start(&rtc->pie_timer, period,
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HRTIMER_MODE_REL);
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if (rtc->pie_enabled && rtc_update_hrtimer(rtc, 1) < 0) {
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spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
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cpu_relax();
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goto retry;
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}
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}
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spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
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