From 53cc2820acbdbcc768675bfaff321f3a8680a317 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 22 Jul 2011 09:12:50 +0000 Subject: [PATCH 1/3] rtc: Handle errors correctly in rtc_irq_set_state() In rtc_irq_set_state, the code checks the correctness of the parameters, but then goes on to unconditionally arms/disarms the hrtimer. Thus a random task might arm/disarm rtc timer and surprise the real owner by either generating events or by stopping them. Cc: stable@kernel.org Signed-off-by: Thomas Gleixner Signed-off-by: John Stultz --- drivers/rtc/interface.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c index df68618f6dbb..b6bf57f25cc9 100644 --- a/drivers/rtc/interface.c +++ b/drivers/rtc/interface.c @@ -656,6 +656,8 @@ int rtc_irq_set_state(struct rtc_device *rtc, struct rtc_task *task, int enabled 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); @@ -664,6 +666,7 @@ int rtc_irq_set_state(struct rtc_device *rtc, struct rtc_task *task, int enabled hrtimer_cancel(&rtc->pie_timer); } rtc->pie_enabled = enabled; +out: spin_unlock_irqrestore(&rtc->irq_task_lock, flags); return err; From 3c8bb90efb6e3105206e4aaa9127395feeda5492 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 22 Jul 2011 09:12:51 +0000 Subject: [PATCH 2/3] 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 Signed-off-by: Thomas Gleixner Signed-off-by: John Stultz --- drivers/rtc/interface.c | 56 +++++++++++++++++++++++++++-------------- 1 file changed, 37 insertions(+), 19 deletions(-) diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c index b6bf57f25cc9..a1ba2caa8308 100644 --- a/drivers/rtc/interface.c +++ b/drivers/rtc/interface.c @@ -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 always cancel the timer here first, 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) 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); From 6e7a333eaa522ef73be01caec7a01521490aaf00 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 22 Jul 2011 09:12:51 +0000 Subject: [PATCH 3/3] rtc: Limit RTC PIE frequency The RTC pie hrtimer is self rearming. We really need to limit the frequency to something sensible. Thus limit it to the 8192Hz max value from the rtc man documentation Cc: Willy Tarreau Cc: stable@kernel.org Signed-off-by: Thomas Gleixner [jstultz: slightly reworked to use RTC_MAX_FREQ value] Signed-off-by: John Stultz --- drivers/rtc/interface.c | 2 +- include/linux/rtc.h | 3 +++ 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c index a1ba2caa8308..44e91e598f8d 100644 --- a/drivers/rtc/interface.c +++ b/drivers/rtc/interface.c @@ -708,7 +708,7 @@ int rtc_irq_set_freq(struct rtc_device *rtc, struct rtc_task *task, int freq) int err = 0; unsigned long flags; - if (freq <= 0) + if (freq <= 0 || freq > RTC_MAX_FREQ) return -EINVAL; retry: spin_lock_irqsave(&rtc->irq_task_lock, flags); diff --git a/include/linux/rtc.h b/include/linux/rtc.h index b27ebea25660..93f4d035076b 100644 --- a/include/linux/rtc.h +++ b/include/linux/rtc.h @@ -97,6 +97,9 @@ struct rtc_pll_info { #define RTC_AF 0x20 /* Alarm interrupt */ #define RTC_UF 0x10 /* Update interrupt for 1Hz RTC */ + +#define RTC_MAX_FREQ 8192 + #ifdef __KERNEL__ #include