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rcu: Remove redundant memory barrier from __call_rcu() 

The first memory barrier in __call_rcu() is supposed to order any
updates done beforehand by the caller against the actual queuing
of the callback.  However, the second memory barrier (which is intended
to order incrementing the queue lengths before queuing the callback)
is also between the caller's updates and the queuing of the callback.
The second memory barrier can therefore serve both purposes.

This commit therefore removes the first memory barrier.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2012-08-13 16:34:12 -07:00 committed by Paul E. McKenney
parent c96ea7cfdd
commit fdab649b1a
1 changed files with 0 additions and 2 deletions
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2
kernel/rcutree.c
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@ -1922,8 +1922,6 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
head->func = func;
head->next = NULL;
smp_mb(); /* Ensure RCU update seen before callback registry. */
/*
* Opportunistically note grace-period endings and beginnings.
* Note that we might see a beginning right after we see an