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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0

* Ingo Molnar <mingo@elte.hu> wrote:

> > Oct 26 21:43:56 porky kernel: BUG: sleeping function called from
> > invalid context amlat(3963) at kernel/mutex.c:28
> > Oct 26 21:43:56 porky kernel: in_atomic():1 [00000001], irqs_disabled():1
> > Oct 26 21:43:56 porky kernel: [<c011c7da>] __might_sleep+0xca/0xe0 (12)
> > Oct 26 21:43:56 porky kernel: [<c0137d89>] _mutex_lock+0x39/0x50 (36)
> > Oct 26 21:43:56 porky kernel: [<c0137df6>] _mutex_lock_irqsave+0x16/0x20 (24)
> > Oct 26 21:43:56 porky kernel: [<c012977d>] __mod_timer+0x4d/0x1f0 (12)
> > Oct 26 21:43:56 porky kernel: [<c01f6535>] rtc_do_ioctl+0x185/0x970 (44)
>
> does the quick hack below help?

here's a more complete fix.

Ingo

--- linux/drivers/char/rtc.c.orig
+++ linux/drivers/char/rtc.c
@@ -177,7 +177,7 @@ static unsigned long rtc_max_user_freq =
/*
* rtc_task_lock nests inside rtc_lock.
*/
-static DECLARE_SPINLOCK(rtc_task_lock);
+static DECLARE_RAW_SPINLOCK(rtc_task_lock);
static rtc_task_t *rtc_callback = NULL;
#endif

@@ -238,10 +238,17 @@ irqreturn_t rtc_interrupt(int irq, void
rtc_irq_data |= (CMOS_READ(RTC_INTR_FLAGS) & 0xF0);
}

- if (rtc_status & RTC_TIMER_ON)
+ if (rtc_status & RTC_TIMER_ON) {
+ spin_unlock (&rtc_lock);
+ /*
+ * We do the mod_timer outside of the lock because
+ * it may reschedule under PREEMPT_REALTIME. As long
+ * as we read the flag race-free it is not a problem
+ * if two mod_timer()s race:
+ */
mod_timer(&rtc_irq_timer, jiffies + HZ/rtc_freq + 2*HZ/100);
-
- spin_unlock (&rtc_lock);
+ } else
+ spin_unlock (&rtc_lock);

/* Now do the rest of the actions */
spin_lock(&rtc_task_lock);
@@ -1094,17 +1101,19 @@ static void rtc_dropped_irq(unsigned lon
return;
}

- /* Just in case someone disabled the timer from behind our back... */
- if (rtc_status & RTC_TIMER_ON)
- mod_timer(&rtc_irq_timer, jiffies + HZ/rtc_freq + 2*HZ/100);
-
rtc_irq_data += ((rtc_freq/HZ)<<8);
rtc_irq_data &= ~0xff;
rtc_irq_data |= (CMOS_READ(RTC_INTR_FLAGS) & 0xF0); /* restart */

freq = rtc_freq;

- spin_unlock_irq(&rtc_lock);
+ /* Just in case someone disabled the timer from behind our back... */
+ if (rtc_status & RTC_TIMER_ON) {
+ spin_unlock_irq(&rtc_lock);
+ mod_timer(&rtc_irq_timer, jiffies + HZ/rtc_freq + 2*HZ/100);
+ } else
+ spin_unlock_irq(&rtc_lock);
+

printk(KERN_WARNING "rtc: lost some interrupts at %ldHz.\n", freq);

-
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