[PATCH 3/5] rcusync: introduce rcu_sync_dtor()

[Oleg Nesterov <oleg@redhat.com>]

Add the new rcu_sync_ops->wait() method and the new helper,
rcu_sync_dtor().

It is needed if you are going to, say, kfree(rcu_sync_object).
It simply calls ops->wait() to "flush" the potentially pending
rcu callback.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/rcusync.h |    2 ++
 kernel/rcusync.c        |   21 +++++++++++++++++++++
 2 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/include/linux/rcusync.h b/include/linux/rcusync.h
index ab787c1..33864a0 100644
--- a/include/linux/rcusync.h
+++ b/include/linux/rcusync.h
@@ -7,6 +7,7 @@
 struct rcu_sync_ops {
 	void (*sync)(void);
 	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+	void (*wait)(void);
 #ifdef CONFIG_PROVE_RCU
 	int (*held)(void);
 #endif
@@ -36,6 +37,7 @@ 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 *);
+extern void rcu_sync_dtor(struct rcu_sync_struct *);
 
 extern struct rcu_sync_ops rcu_sync_ops_array[];
 
diff --git a/kernel/rcusync.c b/kernel/rcusync.c
index 21cde9b..bb311eb 100644
--- a/kernel/rcusync.c
+++ b/kernel/rcusync.c
@@ -16,16 +16,19 @@ struct rcu_sync_ops rcu_sync_ops_array[] = {
 	[RCU_SYNC] = {
 		.sync = synchronize_rcu,
 		.call = call_rcu,
+		.wait = rcu_barrier,
 		__INIT_HELD(rcu_read_lock_held)
 	},
 	[RCU_SCHED_SYNC] = {
 		.sync = synchronize_sched,
 		.call = call_rcu_sched,
+		.wait = rcu_barrier_sched,
 		__INIT_HELD(rcu_read_lock_sched_held)
 	},
 	[RCU_BH_SYNC] = {
 		.sync = synchronize_rcu_bh,
 		.call = call_rcu_bh,
+		.wait = rcu_barrier_bh,
 		__INIT_HELD(rcu_read_lock_bh_held)
 	},
 };
@@ -113,3 +116,21 @@ void rcu_sync_exit(struct rcu_sync_struct *rss)
 	}
 	spin_unlock_irq(&rss->rss_lock);
 }
+
+void rcu_sync_dtor(struct rcu_sync_struct *rss)
+{
+	int cb_state;
+
+	BUG_ON(rss->gp_count);
+
+	spin_lock_irq(&rss->rss_lock);
+	if (rss->cb_state == CB_REPLAY)
+		rss->cb_state = CB_PENDING;
+	cb_state = rss->cb_state;
+	spin_unlock_irq(&rss->rss_lock);
+
+	if (cb_state != CB_IDLE) {
+		rss->ops->wait();
+		BUG_ON(rss->cb_state != CB_IDLE);
+	}
+}
-- 
1.5.5.1