On 12/09, Paul E. McKenney wrote:
>
> This commit therefore adds a smp_mb__after_unlock_lock(), which may be
> placed after a LOCK primitive to restore the full-memory-barrier semantic.
> All definitions are currently no-ops, but will be upgraded for some
> architectures when queued locks arrive.
I am wondering, perhaps smp_mb__after_unlock() makes more sense?
Note that it already has the potential user:
--- x/kernel/sched/wait.c
+++ x/kernel/sched/wait.c
@@ -176,8 +176,9 @@ prepare_to_wait(wait_queue_head_t *q, wa
spin_lock_irqsave(&q->lock, flags);
if (list_empty(&wait->task_list))
__add_wait_queue(q, wait);
- set_current_state(state);
+ __set_current_state(state);
spin_unlock_irqrestore(&q->lock, flags);
+ smp_mb__after_unlock();
}
EXPORT_SYMBOL(prepare_to_wait);
@@ -190,8 +191,9 @@ prepare_to_wait_exclusive(wait_queue_hea
spin_lock_irqsave(&q->lock, flags);
if (list_empty(&wait->task_list))
__add_wait_queue_tail(q, wait);
- set_current_state(state);
+ __set_current_state(state);
spin_unlock_irqrestore(&q->lock, flags);
+ smp_mb__after_unlock();
}
EXPORT_SYMBOL(prepare_to_wait_exclusive);
Assuming it can also be used "later", after another LOCK, like in
your example in 5/7.
Oleg.
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