Messages in this thread Patch in this message | | | Date | Tue, 10 Dec 2013 18:04:04 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH v5 tip/core/locking 6/7] locking: Add an smp_mb__after_unlock_lock() for UNLOCK+LOCK barrier |
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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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