On Wed, May 07, 2008 at 08:31:05AM -0700, Andrew Morton wrote:
I can't figure it out either. Unless schedule() is broken somehow ...
but that should have shown up with semaphore-sleepers.c, shouldn't it?
One other difference between semaphore-sleepers and the new generic code
is that in effect, semaphore-sleepers does a little bit of spinning
before it sleeps. That is, if up() and down() are called more-or-less
simultaneously, the increment of sem->count will happen before __down
calls schedule(). How about something like this:
diff --git a/kernel/semaphore.c b/kernel/semaphore.c
index 5c2942e..ef83f5a 100644
--- a/kernel/semaphore.c
+++ b/kernel/semaphore.c
@@ -211,6 +211,7 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
waiter.up = 0;
for (;;) {
+ int i;
if (state == TASK_INTERRUPTIBLE && signal_pending(task))
goto interrupted;
if (state == TASK_KILLABLE && fatal_signal_pending(task))
@@ -219,7 +220,15 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
goto timed_out;
__set_task_state(task, state);
spin_unlock_irq(&sem->lock);
+
+ for (i = 0; i < 10; i++) {
+ if (waiter.up)
+ goto skip_schedule;
+ cpu_relax();
+ }
+
timeout = schedule_timeout(timeout);
+ skip_schedule:
spin_lock_irq(&sem->lock);
if (waiter.up)
return 0;
Maybe it'd be enough to test it once ... or maybe we should use
spin_is_locked() ... Ingo?
--
Intel are signing my paycheques ... these opinions are still mine
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
--
