[PATCH] get_offset_pit and do_timer_overflow vs IRQ locking

From: john stultz <johnstul@us.ibm.com>, Alexander Atanasov <alex@ssi.bg>

We want to make sure we update jiffies_p and count_p atomically.  So I'm
inserting the spin_unlock_irqrestore() after we update count_p, rather then
just before.

diff --git a/arch/i386/kernel/timers/timer_pit.c b/arch/i386/kernel/timers/timer_pit.c
index cdcc95b74aaf9bbc14c7f1f34b56a9fecc94cbd1..7d521228c28a7a9e11577f1ebdfa38540ac9c5ef 100644 (file)
--- a/arch/i386/kernel/timers/timer_pit.c
+++ b/arch/i386/kernel/timers/timer_pit.c
@@ -54,7 +54,7 @@ static void delay_pit(unsigned long loops)
 }
 
 
-/* This function must be called with interrupts disabled 
+/* This function must be called with xtime_lock held.
  * It was inspired by Steve McCanne's microtime-i386 for BSD.  -- jrs
  * 
  * However, the pc-audio speaker driver changes the divisor so that
@@ -93,7 +93,7 @@ static unsigned long get_offset_pit(void)
        static unsigned long jiffies_p = 0;
 
        /*
-        * cache volatile jiffies temporarily; we have IRQs turned off. 
+        * cache volatile jiffies temporarily; we have xtime_lock. 
         */
        unsigned long jiffies_t;
 
@@ -119,8 +119,6 @@ static unsigned long get_offset_pit(void)
                 count = LATCH - 1;
         }
        
-       spin_unlock_irqrestore(&i8253_lock, flags);
-
        /*
         * avoiding timer inconsistencies (they are rare, but they happen)...
         * there are two kinds of problems that must be avoided here:
@@ -130,7 +128,6 @@ static unsigned long get_offset_pit(void)
         *     (see c't 95/10 page 335 for Neptun bug.)
         */
 
-
        if( jiffies_t == jiffies_p ) {
                if( count > count_p ) {
                        /* the nutcase */
@@ -141,6 +138,8 @@ static unsigned long get_offset_pit(void)
 
        count_p = count;
 
+       spin_unlock_irqrestore(&i8253_lock, flags);
+
        count = ((LATCH-1) - count) * TICK_SIZE;
        count = (count + LATCH/2) / LATCH;