[PATCH 3/3] srcu: Decrease the srcu size state numbers

[Pingfan Liu <kernelfans@gmail.com>]

With the previous patch, srcu_cb_mutex is held when setting
SRCU_SIZE_WAIT_BARRIER. It means that only two seq snap value can exist.
And these two snaps can not see the active snp tree if
srcu_gp_start_if_needed() fetches the srcu_size_state before it is
updated to SRCU_SIZE_WAIT_BARRIER.

After dispatching these two snap value's callbacks, the mask in
snp->srcu_data_have_cbs[idx] is assured to be right. Hence the size
state following SRCU_SIZE_WAIT_BARRIER can be shrink to three.

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 | 15 +++++++++------
 kernel/rcu/srcutree.c    |  3 ---
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index e3014319d1ad..34cb9435c14d 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -94,13 +94,16 @@ struct srcu_struct {
 /* Values for size state variable (->srcu_size_state). */
 #define SRCU_SIZE_SMALL		0
 #define SRCU_SIZE_ALLOC		1
+/* If snp tree is initialized */
 #define SRCU_SIZE_WAIT_BARRIER	2
-#define SRCU_SIZE_WAIT_CALL	3
-#define SRCU_SIZE_WAIT_CBS1	4
-#define SRCU_SIZE_WAIT_CBS2	5
-#define SRCU_SIZE_WAIT_CBS3	6
-#define SRCU_SIZE_WAIT_CBS4	7
-#define SRCU_SIZE_BIG		8
+/*
+ * The following two states for the in-flight seq snap, who may not see
+ * the snp tree is active.
+ */
+#define SRCU_SIZE_WAIT_CBS1	3
+#define SRCU_SIZE_WAIT_CBS2	4
+/* All seq snap see the active tree */
+#define SRCU_SIZE_BIG		5
 
 /* Values for state variable (bottom bits of ->srcu_gp_seq). */
 #define SRCU_STATE_IDLE		0
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 281cd69fe804..bdf392e2ef63 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1652,11 +1652,8 @@ static const char * const srcu_size_state_name[] = {
 	"SRCU_SIZE_SMALL",
 	"SRCU_SIZE_ALLOC",
 	"SRCU_SIZE_WAIT_BARRIER",
-	"SRCU_SIZE_WAIT_CALL",
 	"SRCU_SIZE_WAIT_CBS1",
 	"SRCU_SIZE_WAIT_CBS2",
-	"SRCU_SIZE_WAIT_CBS3",
-	"SRCU_SIZE_WAIT_CBS4",
 	"SRCU_SIZE_BIG",
 	"SRCU_SIZE_???",
 };
-- 
2.31.1