[PATCH] srcu: Add comments for srcu_size_state

[Pingfan Liu <kernelfans@gmail.com>]

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>,
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Zhang, Qiang1" <qiang1.zhang@intel.com>
To: rcu@vger.kernel.org
---
 include/linux/srcutree.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index d4b7f3daf2f8..ee4f3ffa1cce 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -94,8 +94,16 @@ struct srcu_struct {
 /* Values for size state variable (->srcu_size_state). */
 #define SRCU_SIZE_SMALL		0
 #define SRCU_SIZE_ALLOC		1
+/* snp tree has been initialized */
 #define SRCU_SIZE_WAIT_BARRIER	2
+/* In this state, any srcu_barrier(), which considers the system not using snp
+ * tree, has finished.
+ */
 #define SRCU_SIZE_WAIT_CALL	3
+/*
+ * Before snp tree is used, there can be two GPs , each takes two seq snap values.
+ * Wait until CBS1 - CBS4 elapse so these callbacks finishes.
+ */
 #define SRCU_SIZE_WAIT_CBS1	4
 #define SRCU_SIZE_WAIT_CBS2	5
 #define SRCU_SIZE_WAIT_CBS3	6
-- 
2.31.1