[PATCH 2/5] rcusync: add the CONFIG_PROVE_RCU checks

[Oleg Nesterov <oleg@redhat.com>]

It would be nice to validate that the caller of rcu_sync_is_idle()
holds the corresponding type of RCU read-side lock. Add the new
rcu_sync_ops->held() method and change rcu_sync_is_idle() to
WARN() if it returns false.

This obviously penalizes the readers (fast-path), but only if
CONFIG_PROVE_RCU.

Suggested-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/rcusync.h |    6 ++++++
 kernel/rcusync.c        |    9 +++++++++
 2 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/include/linux/rcusync.h b/include/linux/rcusync.h
index 30c6037..ab787c1 100644
--- a/include/linux/rcusync.h
+++ b/include/linux/rcusync.h
@@ -7,6 +7,9 @@
 struct rcu_sync_ops {
 	void (*sync)(void);
 	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+#ifdef CONFIG_PROVE_RCU
+	int (*held)(void);
+#endif
 };
 
 struct rcu_sync_struct {
@@ -22,6 +25,9 @@ struct rcu_sync_struct {
 
 static inline bool rcu_sync_is_idle(struct rcu_sync_struct *rss)
 {
+#ifdef CONFIG_PROVE_RCU
+	WARN_ON(!rss->ops->held());
+#endif
 	return !rss->gp_state; /* GP_IDLE */
 }
 
diff --git a/kernel/rcusync.c b/kernel/rcusync.c
index 1cefb83..21cde9b 100644
--- a/kernel/rcusync.c
+++ b/kernel/rcusync.c
@@ -6,18 +6,27 @@ enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
 
 #define	rss_lock	gp_wait.lock
 
+#ifdef CONFIG_PROVE_RCU
+#define __INIT_HELD(func)	.held = func,
+#else
+#define __INIT_HELD(func)
+#endif
+
 struct rcu_sync_ops rcu_sync_ops_array[] = {
 	[RCU_SYNC] = {
 		.sync = synchronize_rcu,
 		.call = call_rcu,
+		__INIT_HELD(rcu_read_lock_held)
 	},
 	[RCU_SCHED_SYNC] = {
 		.sync = synchronize_sched,
 		.call = call_rcu_sched,
+		__INIT_HELD(rcu_read_lock_sched_held)
 	},
 	[RCU_BH_SYNC] = {
 		.sync = synchronize_rcu_bh,
 		.call = call_rcu_bh,
+		__INIT_HELD(rcu_read_lock_bh_held)
 	},
 };
 
-- 
1.5.5.1