Re: [PATCH [RT] 05/14] rearrange rt_spin_lock sleep

[Gregory Haskins]

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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