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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().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Ben Greear <greearb@candelatech.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Thomas Gleixner 2011-07-26 16:08:20 -07:00 committed by Linus Torvalds
parent 431e2bcc37
commit b830ac1d9a
1 changed files with 37 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

56
drivers/rtc/interface.c
View File

@ -636,6 +636,29 @@ void rtc_irq_unregister(struct rtc_device *rtc, struct rtc_task *task)
}
EXPORT_SYMBOL_GPL(rtc_irq_unregister);
static int rtc_update_hrtimer(struct rtc_device *rtc, int enabled)
{
/*
* We unconditionally cancel the timer here, because otherwise
* we could run into BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
* when we manage to start the timer before the callback
* returns HRTIMER_RESTART.
*
* We cannot use hrtimer_cancel() here as a running callback
* could be blocked on rtc->irq_task_lock and hrtimer_cancel()
* would spin forever.
*/
if (hrtimer_try_to_cancel(&rtc->pie_timer) < 0)
return -1;
if (enabled) {
ktime_t period = ktime_set(0, NSEC_PER_SEC / rtc->irq_freq);
hrtimer_start(&rtc->pie_timer, period, HRTIMER_MODE_REL);
}
return 0;
}
/**
* rtc_irq_set_state - enable/disable 2^N Hz periodic IRQs
* @rtc: the rtc device
@ -651,24 +674,21 @@ int rtc_irq_set_state(struct rtc_device *rtc, struct rtc_task *task, int enabled
int err = 0;
unsigned long flags;
retry:
spin_lock_irqsave(&rtc->irq_task_lock, flags);
if (rtc->irq_task != NULL && task == NULL)
err = -EBUSY;
if (rtc->irq_task != task)
err = -EACCES;
if (err)
goto out;
if (enabled) {
ktime_t period = ktime_set(0, NSEC_PER_SEC/rtc->irq_freq);
hrtimer_start(&rtc->pie_timer, period, HRTIMER_MODE_REL);
} else {
hrtimer_cancel(&rtc->pie_timer);
if (!err) {
if (rtc_update_hrtimer(rtc, enabled) < 0) {
spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
cpu_relax();
goto retry;
}
rtc->pie_enabled = enabled;
}
rtc->pie_enabled = enabled;
out:
spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
return err;
}
EXPORT_SYMBOL_GPL(rtc_irq_set_state);
@ -690,20 +710,18 @@ int rtc_irq_set_freq(struct rtc_device *rtc, struct rtc_task *task, int freq)
if (freq <= 0 || freq > 5000)
return -EINVAL;
retry:
spin_lock_irqsave(&rtc->irq_task_lock, flags);
if (rtc->irq_task != NULL && task == NULL)
err = -EBUSY;
if (rtc->irq_task != task)
err = -EACCES;
if (err == 0) {
if (!err) {
rtc->irq_freq = freq;
if (rtc->pie_enabled) {
ktime_t period;
hrtimer_cancel(&rtc->pie_timer);
period = ktime_set(0, NSEC_PER_SEC/rtc->irq_freq);
hrtimer_start(&rtc->pie_timer, period,
HRTIMER_MODE_REL);
if (rtc->pie_enabled && rtc_update_hrtimer(rtc, 1) < 0) {
spin_unlock_irqrestore(&rtc->irq_task_lock, flags);
cpu_relax();
goto retry;
}
}
spin_unlock_irqrestore(&rtc->irq_task_lock, flags);