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authorPaul E. McKenney <paulmck@kernel.org>2021-04-29 11:18:01 -0700
committerPaul E. McKenney <paulmck@kernel.org>2021-05-13 09:13:23 -0700
commit1893afd63409111c6edcee9d6e1196fc06cf4fd7 (patch)
tree7e69c09686f67289eacdabcd4f25e8471230c93e /kernel/rcu
parent76c8eaafe4f061f3790112842a2fbb297e4bea88 (diff)
rcu: Improve comments describing RCU read-side critical sections
There are a number of places that call out the fact that preempt-disable regions of code now act as RCU read-side critical sections, where preempt-disable regions of code include irq-disable regions of code, bh-disable regions of code, hardirq handlers, and NMI handlers. However, someone relying solely on (for example) the call_rcu() header comment might well have no idea that preempt-disable regions of code have RCU semantics. This commit therefore updates the header comments for call_rcu(), synchronize_rcu(), rcu_dereference_bh_check(), and rcu_dereference_sched_check() to call out these new(ish) forms of RCU readers. Reported-by: Michel Lespinasse <michel@lespinasse.org> [ paulmck: Apply Matthew Wilcox and Michel Lespinasse feedback. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.c24
1 files changed, 14 insertions, 10 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2437960a2795..4b00e4fbfa10 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3059,12 +3059,14 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func)
* 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. In addition, regions of code across which interrupts,
- * preemption, or softirqs have been disabled also serve as RCU read-side
- * critical sections. This includes hardware interrupt handlers, softirq
- * handlers, and NMI handlers.
+ * 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. In addition, but only in
+ * v5.0 and later, regions of code across which interrupts, preemption,
+ * or softirqs have been disabled also serve as RCU read-side critical
+ * sections. This includes hardware interrupt handlers, softirq handlers,
+ * and NMI handlers.
*
* Note that all CPUs must agree that the grace period extended beyond
* all pre-existing RCU read-side critical section. On systems with more
@@ -3730,10 +3732,12 @@ static int rcu_blocking_is_gp(void)
* 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.
- * In addition, regions of code across which interrupts, preemption, or
- * softirqs have been disabled also serve as RCU read-side critical
+ * synchronize_rcu() was waiting.
+ *
+ * RCU read-side critical sections are delimited by rcu_read_lock()
+ * and rcu_read_unlock(), and may be nested. In addition, but only in
+ * v5.0 and later, regions of code across which interrupts, preemption,
+ * or softirqs have been disabled also serve as RCU read-side critical
* sections. This includes hardware interrupt handlers, softirq handlers,
* and NMI handlers.
*