This is a note to let you know that I've just added the patch titled
rtc: fix hrtimer deadlock
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rtc-fix-hrtimer-deadlock.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From b830ac1d9a2262093bb0f3f6a2fd2a1c8278daf5 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <[email protected]>
Date: Tue, 26 Jul 2011 16:08:20 -0700
Subject: rtc: fix hrtimer deadlock
From: Thomas Gleixner <[email protected]>
commit b830ac1d9a2262093bb0f3f6a2fd2a1c8278daf5 upstream.
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 <[email protected]>
Reported-by: Ben Greear <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/rtc/interface.c | 56 +++++++++++++++++++++++++++++++-----------------
1 file changed, 37 insertions(+), 19 deletions(-)
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -636,6 +636,29 @@ void rtc_irq_unregister(struct rtc_devic
}
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
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 *
if (freq <= 0)
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);
Patches currently in stable-queue which might be from [email protected] are
queue-3.0/rtc-fix-hrtimer-deadlock.patch
queue-3.0/rtc-handle-errors-correctly-in-rtc_irq_set_state.patch
queue-3.0/rtc-limit-frequency.patch
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