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

[Ingo Molnar]

* Ingo Molnar <mingo@xxxxxxx> wrote:

> > does the quick hack below help?
> 
> here's a more complete fix.

third time lucky?

	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);
@@ -404,8 +411,8 @@ static int rtc_do_ioctl(unsigned int cmd
 		if (rtc_status & RTC_TIMER_ON) {
 			spin_lock_irq (&rtc_lock);
 			rtc_status &= ~RTC_TIMER_ON;
-			del_timer(&rtc_irq_timer);
 			spin_unlock_irq (&rtc_lock);
+			del_timer(&rtc_irq_timer); // FIXME
 		}
 		return 0;
 	}
@@ -730,9 +737,10 @@ static int rtc_release(struct inode *ino
 	}
 	if (rtc_status & RTC_TIMER_ON) {
 		rtc_status &= ~RTC_TIMER_ON;
-		del_timer(&rtc_irq_timer);
-	}
-	spin_unlock_irq(&rtc_lock);
+		spin_unlock_irq(&rtc_lock);
+		del_timer(&rtc_irq_timer); // FIXME
+	} else
+		spin_unlock_irq(&rtc_lock);
 
 	if (file->f_flags & FASYNC) {
 		rtc_fasync (-1, file, 0);
@@ -808,6 +816,7 @@ int rtc_unregister(rtc_task_t *task)
 	return -EIO;
 #else
 	unsigned char tmp;
+	int rm_timer;
 
 	spin_lock_irq(&rtc_lock);
 	spin_lock(&rtc_task_lock);
@@ -827,13 +836,16 @@ int rtc_unregister(rtc_task_t *task)
 		CMOS_WRITE(tmp, RTC_CONTROL);
 		CMOS_READ(RTC_INTR_FLAGS);
 	}
+	rm_timer = 0;
 	if (rtc_status & RTC_TIMER_ON) {
 		rtc_status &= ~RTC_TIMER_ON;
-		del_timer(&rtc_irq_timer);
+		rm_timer = 1;
 	}
 	rtc_status &= ~RTC_IS_OPEN;
 	spin_unlock(&rtc_task_lock);
 	spin_unlock_irq(&rtc_lock);
+	if (rm_timer)
+		del_timer(&rtc_irq_timer);
 	return 0;
 #endif
 }
@@ -1094,17 +1106,19 @@ 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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