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Subject[PATCH RFC tip/core/rcu 30/30] rcu: improve kerneldoc for rcu_read_lock(), call_rcu(), and synchronize_rcu()
Date
Make it explicit that new RCU read-side critical sections that start
after call_rcu() and synchronize_rcu() start might still be running
after the end of the relevant grace period.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/linux/rcupdate.h | 16 +++++++++-------
kernel/rcutree_plugin.h | 8 +++++---
2 files changed, 14 insertions(+), 10 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 508ebba..27b44b3 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -444,7 +444,7 @@ extern int rcu_my_thread_group_empty(void);
* until after the all the other CPUs exit their critical sections.
*
* Note, however, that RCU callbacks are permitted to run concurrently
- * with RCU read-side critical sections. One way that this can happen
+ * with new RCU read-side critical sections. One way that this can happen
* is via the following sequence of events: (1) CPU 0 enters an RCU
* read-side critical section, (2) CPU 1 invokes call_rcu() to register
* an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
@@ -602,11 +602,13 @@ extern void wakeme_after_rcu(struct rcu_head *head);
/**
* call_rcu() - Queue an RCU callback for invocation after a grace period.
* @head: structure to be used for queueing the RCU updates.
- * @func: actual update function to be invoked after the grace period
+ * @func: actual callback function to be invoked after the grace period
*
- * The update function will be invoked some time after a full grace
- * period elapses, in other words after all currently executing RCU
- * read-side critical sections have completed. RCU read-side critical
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all pre-existing RCU read-side
+ * critical sections have completed. However, the callback function
+ * might well execute concurrently with RCU read-side critical sections
+ * that started after call_rcu() was invoked. RCU read-side critical
* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
* and may be nested.
*/
@@ -616,9 +618,9 @@ extern void call_rcu(struct rcu_head *head,
/**
* call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
* @head: structure to be used for queueing the RCU updates.
- * @func: actual update function to be invoked after the grace period
+ * @func: actual callback function to be invoked after the grace period
*
- * The update function will be invoked some time after a full grace
+ * The callback function will be invoked some time after a full grace
* period elapses, in other words after all currently executing RCU
* read-side critical sections have completed. call_rcu_bh() assumes
* that the read-side critical sections end on completion of a softirq
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 9906f85..63bb771 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -546,9 +546,11 @@ EXPORT_SYMBOL_GPL(call_rcu);
*
* Control will return to the caller some time after a full grace
* period has elapsed, in other words after all currently executing RCU
- * read-side critical sections have completed. RCU read-side critical
- * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
- * and may be nested.
+ * read-side critical sections have completed. Note, however, that
+ * upon return from synchronize_rcu(), the caller might well be executing
+ * 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.
*/
void synchronize_rcu(void)
{
--
1.7.0.6


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