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SubjectRe: [PATCH [RT] 05/14] rearrange rt_spin_lock sleep
Gregory Haskins wrote:
> @@ -732,14 +741,15 @@ rt_spin_lock_slowlock(struct rt_mutex *lock)
>
> debug_rt_mutex_print_deadlock(&waiter);
>
> - schedule_rt_mutex(lock);
> + update_current(TASK_UNINTERRUPTIBLE, &saved_state);

I have a question for everyone out there about this particular part of
the code. Patch 6/14 adds an optimization that is predicated on the
order in which we modify the state==TASK_UNINTERRUPTIBLE vs reading the
waiter.task below.

My assumption is that the xchg() (inside update_current()) acts as an
effective wmb(). If xchg() does not have this property, then this code
is broken and patch 6/14 should also add a:


+ smp_wmb();


> + if (waiter.task)
> + schedule_rt_mutex(lock);
> + else
> + update_current(TASK_RUNNING_MUTEX, &saved_state);
>
> spin_lock_irqsave(&lock->wait_lock, flags);
> current->flags |= saved_flags;
> current->lock_depth = saved_lock_depth;
> - state = xchg(&current->state, TASK_UNINTERRUPTIBLE);
> - if (unlikely(state == TASK_RUNNING))
> - saved_state = TASK_RUNNING;


Does anyone know the answer to this?

Regards,
-Greg


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