From: Alexander Atanasov <alex@ssi.bg> and John Stultz
Spin lock debugging got this on UP+preempt:
arch/i386/kernel/i8259.c:176:spin_lock(arch/i386/kernel/i8259.c:c03d4838)
already locked by include/asm-i386/mach-default/do_timer.h/50
include/asm-i386/mach-default/do_timer.h:56:
spin_unlock(arch/i386/kernel/i8259.c:c03d4838) not locked
arch/i386/kernel/i8259.c:176:spin_lock(arch/i386/kernel/i8259.c:c03d4838)
already locked by include/asm-i386/mach-default/do_timer.h/50
include/asm-i386/mach-default/do_timer.h:56:
spin_unlock(arch/i386/kernel/i8259.c:c03d4838) not locked
This is due to do_timer_overflow expecting to be called with IRQs disabled,
the whole path used to do that until converted to xtime_lock, but
do_timer_overflow seems to be missed. Patch changes get_offset_pit to hold
i8253_lock while calling do_timer_overflow.
John made some changes and then stress-tested it on 8-way.
arch/i386/kernel/timers/timer_pit.c | 25 +++++++++++++------------
1 files changed, 13 insertions(+), 12 deletions(-)
diff -puN arch/i386/kernel/timers/timer_pit.c~do_timer_overflow-locking-fix arch/i386/kernel/timers/timer_pit.c
--- 25/arch/i386/kernel/timers/timer_pit.c~do_timer_overflow-locking-fix 2003-04-17 19:31:48.000000000 -0700
+++ 25-akpm/arch/i386/kernel/timers/timer_pit.c 2003-04-17 19:33:20.000000000 -0700
@@ -54,7 +54,7 @@ static void delay_pit(unsigned long loop
}
-/* 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;
@@ -110,15 +110,15 @@ static unsigned long get_offset_pit(void
jiffies_t = jiffies;
count |= inb_p(PIT_CH0) << 8;
-
- /* VIA686a test code... reset the latch if count > max + 1 */
- if (count > LATCH) {
- outb_p(0x34, PIT_MODE);
- outb_p(LATCH & 0xff, PIT_CH0);
- outb(LATCH >> 8, PIT_CH0);
- count = LATCH - 1;
- }
-
+
+ /* VIA686a test code... reset the latch if count > max + 1 */
+ if (count > LATCH) {
+ outb_p(0x34, PIT_MODE);
+ outb_p(LATCH & 0xff, PIT_CH0);
+ outb(LATCH >> 8, PIT_CH0);
+ count = LATCH - 1;
+ }
+
spin_unlock_irqrestore(&i8253_lock, flags);
/*
@@ -130,7 +130,6 @@ 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 */
@@ -139,6 +138,8 @@ static unsigned long get_offset_pit(void
} else
jiffies_p = jiffies_t;
+ spin_unlock_irqrestore(&i8253_lock, flags);
+
count_p = count;
count = ((LATCH-1) - count) * TICK_SIZE;
_