rcu_sync: Simplify rcu_sync using new rcu_sync_ops structure

This commit adds the new struct rcu_sync_ops which holds sync/call
methods, and turns the function pointers in rcu_sync_struct into an array
of struct rcu_sync_ops.  This simplifies the "init" helpers by collapsing
a switch statement and explicit multiple definitions into a simple
assignment and a helper macro, respectively.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

2 files changed, 45 insertions, 57 deletions

diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
index cb044df2e21c..c6d2272c4459 100644
--- a/include/linux/rcu_sync.h
+++ b/include/linux/rcu_sync.h
@@ -26,6 +26,8 @@
 #include <linux/wait.h>
 #include <linux/rcupdate.h>
 
+enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
+
 /* Structure to mediate between updaters and fastpath-using readers.  */
 struct rcu_sync {
         int                     gp_state;
@@ -35,43 +37,9 @@ struct rcu_sync {
         int                     cb_state;
         struct rcu_head         cb_head;
 
-        void (*sync)(void);
-        void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+        enum rcu_sync_type      gp_type;
 };
 
-#define ___RCU_SYNC_INIT(name)                                          \
-        .gp_state = 0,                                                  \
-        .gp_count = 0,                                                  \
-        .gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait),         \
-        .cb_state = 0
-
-#define __RCU_SCHED_SYNC_INIT(name) {                                   \
-        ___RCU_SYNC_INIT(name),                                         \
-        .sync = synchronize_sched,                                      \
-        .call = call_rcu_sched,                                         \
-}
-
-#define __RCU_BH_SYNC_INIT(name) {                                      \
-        ___RCU_SYNC_INIT(name),                                         \
-        .sync = synchronize_rcu_bh,                                     \
-        .call = call_rcu_bh,                                            \
-}
-
-#define __RCU_SYNC_INIT(name) {                                         \
-        ___RCU_SYNC_INIT(name),                                         \
-        .sync = synchronize_rcu,                                        \
-        .call = call_rcu,                                               \
-}
-
-#define DEFINE_RCU_SCHED_SYNC(name)                                     \
-        struct rcu_sync name = __RCU_SCHED_SYNC_INIT(name)
-
-#define DEFINE_RCU_BH_SYNC(name)                                        \
-        struct rcu_sync name = __RCU_BH_SYNC_INIT(name)
-
-#define DEFINE_RCU_SYNC(name)                                           \
-        struct rcu_sync name = __RCU_SYNC_INIT(name)
-
 /**
  * rcu_sync_is_idle() - Are readers permitted to use their fastpaths?
  * @rsp: Pointer to rcu_sync structure to use for synchronization
@@ -85,10 +53,28 @@ static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
         return !rsp->gp_state; /* GP_IDLE */
 }
 
-enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
-
 extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type);
 extern void rcu_sync_enter(struct rcu_sync *);
 extern void rcu_sync_exit(struct rcu_sync *);
 
+#define __RCU_SYNC_INITIALIZER(name, type) {                            \
+                .gp_state = 0,                                          \
+                .gp_count = 0,                                          \
+                .gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait), \
+                .cb_state = 0,                                          \
+                .gp_type = type,                                        \
+        }
+
+#define __DEFINE_RCU_SYNC(name, type)   \
+        struct rcu_sync_struct name = __RCU_SYNC_INITIALIZER(name, type)
+
+#define DEFINE_RCU_SYNC(name)           \
+        __DEFINE_RCU_SYNC(name, RCU_SYNC)
+
+#define DEFINE_RCU_SCHED_SYNC(name)     \
+        __DEFINE_RCU_SYNC(name, RCU_SCHED_SYNC)
+
+#define DEFINE_RCU_BH_SYNC(name)        \
+        __DEFINE_RCU_SYNC(name, RCU_BH_SYNC)
+
 #endif /* _LINUX_RCU_SYNC_H_ */
diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
index 0a11df43be23..5a9aa4c394f1 100644
--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -23,6 +23,24 @@
 #include <linux/rcu_sync.h>
 #include <linux/sched.h>
 
+static const struct {
+        void (*sync)(void);
+        void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+} gp_ops[] = {
+        [RCU_SYNC] = {
+                .sync = synchronize_rcu,
+                .call = call_rcu,
+        },
+        [RCU_SCHED_SYNC] = {
+                .sync = synchronize_sched,
+                .call = call_rcu_sched,
+        },
+        [RCU_BH_SYNC] = {
+                .sync = synchronize_rcu_bh,
+                .call = call_rcu_bh,
+        },
+};
+
 enum { GP_IDLE = 0, GP_PENDING, GP_PASSED };
 enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
 
@@ -37,23 +55,7 @@ void rcu_sync_init(struct rcu_sync *rsp, enum rcu_sync_type type)
 {
         memset(rsp, 0, sizeof(*rsp));
         init_waitqueue_head(&rsp->gp_wait);
-
-        switch (type) {
-        case RCU_SYNC:
-                rsp->sync = synchronize_rcu;
-                rsp->call = call_rcu;
-                break;
-
-        case RCU_SCHED_SYNC:
-                rsp->sync = synchronize_sched;
-                rsp->call = call_rcu_sched;
-                break;
-
-        case RCU_BH_SYNC:
-                rsp->sync = synchronize_rcu_bh;
-                rsp->call = call_rcu_bh;
-                break;
-        }
+        rsp->gp_type = type;
 }
 
 /**
@@ -85,7 +87,7 @@ void rcu_sync_enter(struct rcu_sync *rsp)
         BUG_ON(need_wait && need_sync);
 
         if (need_sync) {
-                rsp->sync();
+                gp_ops[rsp->gp_type].sync();
                 rsp->gp_state = GP_PASSED;
                 wake_up_all(&rsp->gp_wait);
         } else if (need_wait) {
@@ -138,7 +140,7 @@ static void rcu_sync_func(struct rcu_head *rcu)
                  * to catch a later GP.
                  */
                 rsp->cb_state = CB_PENDING;
-                rsp->call(&rsp->cb_head, rcu_sync_func);
+                gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
         } else {
                 /*
                  * We're at least a GP after rcu_sync_exit(); eveybody will now
@@ -166,7 +168,7 @@ void rcu_sync_exit(struct rcu_sync *rsp)
         if (!--rsp->gp_count) {
                 if (rsp->cb_state == CB_IDLE) {
                         rsp->cb_state = CB_PENDING;
-                        rsp->call(&rsp->cb_head, rcu_sync_func);
+                        gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
                 } else if (rsp->cb_state == CB_PENDING) {
                         rsp->cb_state = CB_REPLAY;
                 }