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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-10-23 13:47:01 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-11-13 14:08:23 -0800
commitf0a0e6f282c72247e7c8ec17c68d528c1bb4d49e (patch)
tree22b66fc8ac9b95586866ddb447dcc8712d441c14 /kernel/rcutree_plugin.h
parent67afeed2cab0e59712b4ebf1aef9a2e555a188ce (diff)
rcu: Clarify memory-ordering properties of grace-period primitives
This commit explicitly states the memory-ordering properties of the RCU grace-period primitives. Although these properties were in some sense implied by the fundmental property of RCU ("a grace period must wait for all pre-existing RCU read-side critical sections to complete"), stating it explicitly will be a great labor-saving device. Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Diffstat (limited to 'kernel/rcutree_plugin.h')
-rw-r--r--kernel/rcutree_plugin.h8
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f92115488187..57e0ef8ed721 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -670,6 +670,9 @@ EXPORT_SYMBOL_GPL(kfree_call_rcu);
* concurrently with new RCU read-side critical sections that began while
* synchronize_rcu() was waiting. RCU read-side critical sections are
* delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
+ *
+ * See the description of synchronize_sched() for more detailed information
+ * on memory ordering guarantees.
*/
void synchronize_rcu(void)
{
@@ -875,6 +878,11 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
/**
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
+ *
+ * Note that this primitive does not necessarily wait for an RCU grace period
+ * to complete. For example, if there are no RCU callbacks queued anywhere
+ * in the system, then rcu_barrier() is within its rights to return
+ * immediately, without waiting for anything, much less an RCU grace period.
*/
void rcu_barrier(void)
{