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Subject[RFC][PATCH 2/5] rcusync: Introduce struct rcu_sync_ops
From: Oleg Nesterov <oleg@redhat.com>

Add the new struct rcu_sync_ops which holds sync/call methods, and
turn the function pointers in rcu_sync_struct into an array of struct
rcu_sync_ops.

This simplifies the "init" helpers, and this way it is simpler to add
the new methods we need, especially ifdef'ed.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/rcusync.h | 60 ++++++++++++++++++------------------------------
kernel/rcu/sync.c | 43 +++++++++++++++++-----------------
2 files changed, 45 insertions(+), 58 deletions(-)

--- a/include/linux/rcusync.h
+++ b/include/linux/rcusync.h
@@ -4,6 +4,8 @@
#include <linux/wait.h>
#include <linux/rcupdate.h>

+enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
+
struct rcu_sync_struct {
int gp_state;
int gp_count;
@@ -12,53 +14,37 @@ struct rcu_sync_struct {
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_struct name = __RCU_SCHED_SYNC_INIT(name)
-
-#define DEFINE_RCU_BH_SYNC(name) \
- struct rcu_sync_struct name = __RCU_BH_SYNC_INIT(name)
-
-#define DEFINE_RCU_SYNC(name) \
- struct rcu_sync_struct name = __RCU_SYNC_INIT(name)
-
static inline bool rcu_sync_is_idle(struct rcu_sync_struct *rss)
{
return !rss->gp_state; /* GP_IDLE */
}

-enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
-
extern void rcu_sync_init(struct rcu_sync_struct *, enum rcu_sync_type);
extern void rcu_sync_enter(struct rcu_sync_struct *);
extern void rcu_sync_exit(struct rcu_sync_struct *);

+#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_RCUSYNC_H_ */

--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -1,7 +1,24 @@
-
#include <linux/rcusync.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 };

@@ -11,23 +28,7 @@ void rcu_sync_init(struct rcu_sync_struc
{
memset(rss, 0, sizeof(*rss));
init_waitqueue_head(&rss->gp_wait);
-
- switch (type) {
- case RCU_SYNC:
- rss->sync = synchronize_rcu;
- rss->call = call_rcu;
- break;
-
- case RCU_SCHED_SYNC:
- rss->sync = synchronize_sched;
- rss->call = call_rcu_sched;
- break;
-
- case RCU_BH_SYNC:
- rss->sync = synchronize_rcu_bh;
- rss->call = call_rcu_bh;
- break;
- }
+ rss->gp_type = type;
}

void rcu_sync_enter(struct rcu_sync_struct *rss)
@@ -44,7 +45,7 @@ void rcu_sync_enter(struct rcu_sync_stru
BUG_ON(need_wait && need_sync);

if (need_sync) {
- rss->sync();
+ gp_ops[rss->gp_type].sync();
rss->gp_state = GP_PASSED;
wake_up_all(&rss->gp_wait);
} else if (need_wait) {
@@ -81,7 +82,7 @@ static void rcu_sync_func(struct rcu_hea
* to catch a later GP.
*/
rss->cb_state = CB_PENDING;
- rss->call(&rss->cb_head, rcu_sync_func);
+ gp_ops[rss->gp_type].call(&rss->cb_head, rcu_sync_func);
} else {
/*
* We're at least a GP after rcu_sync_exit(); eveybody will now
@@ -99,7 +100,7 @@ void rcu_sync_exit(struct rcu_sync_struc
if (!--rss->gp_count) {
if (rss->cb_state == CB_IDLE) {
rss->cb_state = CB_PENDING;
- rss->call(&rss->cb_head, rcu_sync_func);
+ gp_ops[rss->gp_type].call(&rss->cb_head, rcu_sync_func);
} else if (rss->cb_state == CB_PENDING) {
rss->cb_state = CB_REPLAY;
}



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