| Date | Fri, 22 Feb 2008 08:29:20 -0500 | From | Gregory Haskins <> | Subject | Re: [PATCH [RT] 05/14] rearrange rt_spin_lock sleep |
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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(¤t->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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