[RFC PATCH 02/12] rcu: Turn enabled/offload states into a common flag

[Frederic Weisbecker]

Gather the segcblist properties in a common map to avoid spreading
booleans in the structure. And this prepares for the offloaded state to
be mutable on runtime.

Inspired-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
---
 include/linux/rcu_segcblist.h |  6 ++++--
 kernel/rcu/rcu_segcblist.c    |  6 +++---
 kernel/rcu/rcu_segcblist.h    | 23 +++++++++++++++++++++--
 3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h
index b36afe7b22c9..dca2f39ee67f 100644
--- a/include/linux/rcu_segcblist.h
+++ b/include/linux/rcu_segcblist.h
@@ -63,6 +63,9 @@ struct rcu_cblist {
 #define RCU_NEXT_TAIL		3
 #define RCU_CBLIST_NSEGS	4
 
+#define SEGCBLIST_ENABLED	BIT(0)
+#define SEGCBLIST_OFFLOADED	BIT(1)
+
 struct rcu_segcblist {
 	struct rcu_head *head;
 	struct rcu_head **tails[RCU_CBLIST_NSEGS];
@@ -72,8 +75,7 @@ struct rcu_segcblist {
 #else
 	long len;
 #endif
-	u8 enabled;
-	u8 offloaded;
+	u8 flags;
 };
 
 #define RCU_SEGCBLIST_INITIALIZER(n) \
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 9a0f66133b4b..d131ef8940a0 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -152,7 +152,7 @@ void rcu_segcblist_init(struct rcu_segcblist *rsclp)
 	for (i = 0; i < RCU_CBLIST_NSEGS; i++)
 		rsclp->tails[i] = &rsclp->head;
 	rcu_segcblist_set_len(rsclp, 0);
-	rsclp->enabled = 1;
+	rcu_segcblist_set_flags(rsclp, SEGCBLIST_ENABLED);
 }
 
 /*
@@ -163,7 +163,7 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
 {
 	WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
 	WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
-	rsclp->enabled = 0;
+	rcu_segcblist_clear_flags(rsclp, SEGCBLIST_ENABLED);
 }
 
 /*
@@ -172,7 +172,7 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
  */
 void rcu_segcblist_offload(struct rcu_segcblist *rsclp)
 {
-	rsclp->offloaded = 1;
+	rcu_segcblist_set_flags(rsclp, SEGCBLIST_OFFLOADED);
 }
 
 /*
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 492262bcb591..fc98761e3ee9 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -50,19 +50,38 @@ static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
 #endif
 }
 
+static inline void rcu_segcblist_set_flags(struct rcu_segcblist *rsclp,
+					   int flags)
+{
+	rsclp->flags |= flags;
+}
+
+static inline void rcu_segcblist_clear_flags(struct rcu_segcblist *rsclp,
+					     int flags)
+{
+	rsclp->flags &= ~flags;
+}
+
+static inline bool rcu_segcblist_test_flags(struct rcu_segcblist *rsclp,
+					    int flags)
+{
+	return READ_ONCE(rsclp->flags) & flags;
+}
+
 /*
  * Is the specified rcu_segcblist enabled, for example, not corresponding
  * to an offline CPU?
  */
 static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
 {
-	return rsclp->enabled;
+	return rcu_segcblist_test_flags(rsclp, SEGCBLIST_ENABLED);
 }
 
 /* Is the specified rcu_segcblist offloaded?  */
 static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
 {
-	return IS_ENABLED(CONFIG_RCU_NOCB_CPU) && rsclp->offloaded;
+	return IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
+		rcu_segcblist_test_flags(rsclp, SEGCBLIST_OFFLOADED);
 }
 
 /*
-- 
2.28.0