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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2012-10-23 13:47:01 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2012-11-13 14:08:23 -0800 |
| commit | f0a0e6f282c72247e7c8ec17c68d528c1bb4d49e (patch) | |
| tree | 22b66fc8ac9b95586866ddb447dcc8712d441c14 /kernel/rcutree_plugin.h | |
| parent | 67afeed2cab0e59712b4ebf1aef9a2e555a188ce (diff) | |
| download | lwn-f0a0e6f282c72247e7c8ec17c68d528c1bb4d49e.tar.gz lwn-f0a0e6f282c72247e7c8ec17c68d528c1bb4d49e.zip | |
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.h | 8 |
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) { |